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How to turn any tune into a computer program
BASIC PROGRAMMING 51
MORE SORTING METHODS
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QUERIES: When writing in, please give the make and model of your computer,as well as the Part No., page and line where the program is rejected or where it does not work. We can only answer specific queries– and please do not telephone. Send Special sound effects based on a simple command your queries to INPUT Queries, Marshall Cavendish Partworks Ltd, 58 Old Compton Street, London W IV SPA. INDEX The last part of INPUT, Part 52, will contain a complete, cross-referenced index. For easy access to your growing collection, a cumulative index to the contents INPUT IS SPECIALLY DESIGNED FOR: of each issue is contained on the inside back cover. The SINCLAIR ZX SPECTRUM (16K, 48K,128 and +), COMMODORE 64 and 128, ACORN ELECTRON, BBC B PICTURE CREDITS and B+, and the DRAGON 32 and 64. Front cover, Paul Chave/Ian Stephen. Pages 701, 706, Phil Dobson. Pages 702, 703, 704, 705, 706, Berry Fallon Design. Page 709, Paul Chave/Spectrum. Page In addition, many of the programs and explanations are also 710, Sporting Pictures. Page 712, Will Stephen. Page 715, Kevin O'Brien. Pages suitable for the SINCLAIR ZX81, COMMODORE VIC 20, and 716, 718, Paul Chave/ Ian Stephen. Page 720, 727, Peter Reilly. Page 721, Grant Simon. Page 723, Grant Simon/Ian Stephen. Page 724, Tudor Artists. Pages TANDY COLOUR COMPUTER in 32K with extended BASIC. 728, 730, Jeremy Gower. Programs and text which are specifically for particular machines are indicated by the following symbols: © Marshall Cavendish Limited 1984/5/6 All worldwide rights reserved. SPECTRUM 16K, The contents of this publication including software, codes, listings, 48K,128, and + COMMODORE 64 and 128 graphics, illustrations and text are the exclusive property and copyright of Marshall Cavendish Limited and may not be copied, reproduced, ACORN ELECTRON, transmitted, hired, lent, distributed, stored or modified in any form BBC B and B+ UDRAGON 32 and 64 whatsoever without the prior approval of the Copyright holder. friM: T TANDY TRS80 Published by Marshall Cavendish Partworks Ltd, 58 Old Compton Street, London WIV 5PA, ZX81 VIC 20 COLOUR COMPUTER England. Printed by Artisan Presss, Leicester and Howard Hunt Litho, London. MUSICAL NOTATION A MUSICAL RULER KEY SIGNATURES ADDING RHYTHM PLAYING A TUNE
The real beauty of computer music so cannot play chords. Vertical lines called is that the machine plays it for you. STANDARD MUSICAL NOTATION `bar lines' divide up the music horizontally Find out how to transcribe any Music is usually written on one or two groups into groups of notes called `bars'; each bar has written music into a program that of five horizontal lines, called 'staves' (the the same duration as any other bar, though singular is 'staff). Various note symbols are each one may be internally divided into any remembers your favourite tunes placed on or between the lines of the staves, number of notes, as long as its total their height indicating the pitch, the order duration is the same as other bars. Music has two main elements—pitch and indicating the order of notes in the piece (they rhythm. The first article on music (pages 669 are played from left to right) and the shape of PITCH INFORMATION to 675) dealt mainly with pitch, which the the symbols indicating the notes' durations. The keyboard program in the last article computer provided subject to which keys you Notes which line up vertically are played turned the computers' keyboards into some- pressed, with you adding a touch of rhythm. together to sound as chords, but the programs thing resembling a musical instrument. While This article not only adds a predetermined in this article play only one voice at a time and the programs worked very well, they are rhythm to the music that the computer plays, inevitably limited because of the small num- but also explains how you can turn any piece ber of keys on a computer keyboard compared of sheet music into the DATA that your with the total number of notes you can use— computer needs to play the written tunes. not to mention the difficulty of fingering them. But there is no reason why you should It can be very confusing, and time- in the table and it's probably easier to use these be confined to the same limits when you use consuming, to translate each note on a sheet of for the Spectrum (where the numbers are tunes in your own programs. music into the pitch and duration values for simple) or the Dragon and Tandy (which use You can quite easily convert any piece of your computer, especially if you cannot read letters). The number for the Commodores written music into the numbers that your music. But there is an easy method. and Acorns are more complicated so it's easier computer needs for each of these notes with- If you look at the diagram, you can see that to use the general scale and then convert them out needing very much knowledge of music: pitch values from 1 to 37 are marked beneath in the program. To find out what to mark on just use the 'musical ruler' described later on each note. These are the basis for the numbers each line, compare the numbers on the dia- in this article. But, first, here is a brief you need in your program. gram to the table, and read off your explanation of some of the basics behind You could refer to this diagram whenever computer's equivalent number. written music. you wanted to 'transcribe' a tune, but even that would mean a lot of time spent compar- SHARPS AND FLATS UNDERSTANDING THE NOTES ing your sheet music to the diagram and Unless you convert only pieces of music Fig. 1 shows a typical piece of written music. finding the right note. A much easier method written in C Major, you will at some time This would just play each note available on a is to have a measure of some sort which you need to transcribe sharps and flats—and these keyboard in a rising succession—a 'chroma- can place over any note on a musical staff, and do not have the same pitch as the natural note. tic' scale. just read off its pitch value for your computer. By looking at the key signature, you can see The large symbols at the extreme left of the what, if any, flats or sharps the tune uses (how staves are called 'clefs': the top one is called A PITCH RULE to understand key signatures is explained the 'treble clef and the lower one the 'bass To make this, all you need to do is to mark a later in this article). Any sharps or flats mean clef'. The clefs simply give the note symbols piece of paper with a musical scale. Luckily, you need to change the values on your ruler. on the staves a pitch—without a clef, the pitch this only takes a minute or so, although you Sharps and flats are the black keys on the of any note on a staff is indeterminate. probably need a different scale for each piece drawing of the keyboard, and their pitch Note symbols are placed either between of music, as the size of the staves can vary. numbers are provided. So, for example, the two lines, or squarely over a line. First, place your paper over the staff, and pitch number of the lowest C sharp is 2 (using Notes above or below the staves are related copy onto it the staff lines showing the the general scale of pitch numbers in the table, to the staves by means of leger lines'; so the possible positions of a note. Then all you do is you can see what this is for your micro). This note Middle C lies on a leger line midway write the pitch number for each note against is the same as the pitch number for D flat, and between the two staves, ..nd the three highest the corresponding mark. This ruler can is between 1 and 3, the pitch numbers for C notes in the diagram are on leger lines above trace pitch values directly off the sheet music. and D. the upper staff, at the righthand end. The actual values for each pitch are given But sharps and flats are not shown on the the staff, after the clef. These marks are called Spectrum Commodore Vic Acorn Dragon/ the key signature. (You should note that the General High Low Tandy words 'key' and 'scale' mean the same, so the scale byte byte key of C Major means the same.) 1 — 12 8 97 192 5 C The absence of a key signature indicates 2 — 11 8 225 197 9 C + that the key is C Major, which is a kind of 3 — 10 9 104 200 13 D `default' key, but a key signature of one or 4 — 9 9 247 203 17 D + more sharps or flats means the piece is in a 5 — 8 10 143 206 21 E different key. In a key signature of one sharp, 6 — 7 11 48 208 25 F the sharp sign is at the position at which the 7 —6 11 218 211 29 F+ note F is placed. Its effect is to sharpen all the 8 — 5 12 143 214 33 G Fs, in all octaves, throughout the piece. 9 — 4 13 78 216 37 G + You may remember from the earlier article 10 — 3 14 24 218 41 A that it's necessary to sharpen the Fs to obtain 11 — 2 14 239 220 45 A + the arrangement of musical intervals for B 12 — 1 15 210 222 49 B Major. The key signature of one sharp 13 0 16 195 224 53 C achieves this, and it's known as the key 14 1 17 195 226 57 C + signature of B Major. So if you're transcrib- 15 2 18 209 227 61 D ing a piece that has some sharps or flats just to 16 3 19 239 229 65 D + the right of the clefs, remember to modify all 17 4 21 31 231 69 E the Fs or Cs, or whatever, for the whole piece, 18 5 22 96 232 73 F and use the corrected pitch number. 19 6 23 181 233 77 F + Fig. 4 shows the first few notes of Pop Goes 20 7 25 30 234 81 G the Weasel in the key of F Major, that is with a 21 8 26 156 235 85 G + key signature of one flat. The pitch numbers 22 9 28 49 236 89 A are shown: notice that the fourth note is B flat, 23 10 29 223 237 93 A + with a pitch number of 23 on the general 24 11 31 165 238 97 B scale. This is where your ruler comes in again. 25 12 33 135 239 101 C If your piece of music contains an F sharp, 26 13 35 134 240 105 C + instead of writing the pitch number for F next 27 14 37 162 N/A 109 D to the F mark on your scale, you should write 28 15 39 223 ,, 113 D + the number for F sharp.
29 16 42 62 )3 117 E By doing this for any sharps or flats in the
30 17 44 193 5) 121 F key signature, sharps and flats become just as
31 18 47 107 15 125 F + easy to transcribe as natural notes. 32 19 50 60 ,, 129 G You should be careful, though: sometimes
33 20 53 57 5) 133 G + you may come across accidental sharps, flats 34 21 56 99 ,, 137 A or naturals—these have priority over a key 35 22 59 190 ,, 141 A + signature. 36 23 63 75 ,, 145 B A MATTER OF TIMING 37 24 67 15 31 149 C Once you've worked out the pitch of each note, the next thing is to work out its duration, staves in the diagram to prevent it from altered. A sharp or flat sign used like this is or how long it sounds for. You'll also have to becoming too cluttered. A sharpened note is known as an accidental. Its effect lasts until notated on a staff with its note symbol the end of the bar it's used in, unless its effect preceded by a 'sharp' sign, (which is like the is cancelled before this point. There's a third computer 'hash' character); a flattened note symbol, called a natural, which cancels a appears on the staff preceded by a 'flat' sign, sharp or flat and restores the note to its un- (which is like a lower case t'). sharpened and un-flattened state. Fig. 3 Fig. 2 shows how the first few notes from shows the first few notes of Oh, I Do Like To middle C, including sharps and flats, are Be Beside The Seaside, including an 'E' shown on the upper staff. Notice that while C sharpened by an accidental and naturalized a sharp and D flat share the same pitch number couple of notes later. and the same black key, they appear at different heights on the staff—since one is a C KEY SIGNATURES that has been raised, and the other is a D that Where the scale in which a piece is played has been lowered. contains a sharp or flat note, this note needs to Individual notes in a piece may be shar- be used instead of the natural every time. To pened or flattened, using the appropriate signify that it is always a sharp or flat, the symbols immediately before the notes to be appropriate sign is marked at the beginning of general pitch. To find the actual pitch num- An important point about the way the bers for each computer you can look at the computers operate applies to all the table given earlier in the article. It also shows programs. Suppose one bar contains a single, the relative duration values. long note, and another contains many short There are several points here about the way notes. In the second case the lines that READ the music is written. Firstly, where three and test the DATA will be executed more times `quavers' (the table shows what the notes are than in the first case, and so the speed at called), occur together, as in bars 9 and 11, for which they are played will fall a little because example, their stems have been joined tog- of the extra operating time. Therefore the ether. Small groups of two, three, or four speed of execution of these lines should be as quavers and semi-quavers are often joined high as possible. This is why there is no test like this, to make it easier to read the music. for the end of DATA. But apart from that, the notes are exactly the A convention could be used in which a note down the duration of rest symbols which same—the joins do not change the pitch or negative number, say, signalled the end of the indicate gaps, or periods of silence between duration of the notes. tune; this would require an extra test in these notes. Fig. 5 is a table that shows the note In bar 8, there is a similar join—but this crucial lines and would make the tune slightly symbols and corresponding rest symbols, time it does change the notes a bit. The join uneven. So the program is just allowed to run with their relative durations. It is a very good here is between just two notes and is a curved out of data, when it stops with an error idea to use relative durations for notes and line instead of a straight one. What it means is message, something that is not normally then choose a tempo which defines their that the notes should be joined together to considered good practice. actual durations at a later stage—that way, sound like one, longer, note. The join is Of course, when you use a tune in your own you can quickly and easily experiment to find known as a tie. You can have ties joining any programs, you can use a FOR ... NEXT loop to the tempo which sounds best. You can see number of notes together. To convert them READ the exact number of pieces of DATA, how this works in practise from the program into computer data, you should add up the which would prevent the error occurring. further on in this article. individual durations of the notes to give one Here are the programs to play the tune Both American and English names for the long note. Three Blind Mice: symbols are given: American names are more logical, though they will be less familiar to PROGRAM DATA a British readers. Generally, the stems on the The pitch and duration numbers you've 10 INPUT "ENTER TEMPO (1 — 50)",t: LET notes may point upwards or downwards, worked out for the tune are put into DATA t=t/100 whichever direction looks neater. statements at the end of the program from 20 IF t < 0.001 OR t>0.5 THEN GOTO 10 The two longest rest symbols are little where they are READ and interpreted as the 30 FOR n = 0 TO 1 STEP 0: READ a,b: BEEP rectangular blocks which lie above or below program runs. The DATA for Three Blind Mice a't,b: NEXT n the middle line of the staff. Following a note has been added to the programs in this way. 100 DATA 6,4,6,2,12,0,6,4,6,2,12,0 or a rest by a dot multiplies its duration by There is enough DATA in each statement for 110 DATA 6,7,4,5,2,5,12,4,6,7,4,5,2,5,10,4,2,7 one and a half; a doubly-dotted note has a two bars except on the Dragon and Tandy. 120 DATA 4,12,2,12,2,11,2,9,2,11 duration one-and-three-quarters the duration Some convention of this type is sensible, as it 130 DATA 4,12,2,7,4,7,2,7 of the undotted note. lets you find the DATA for a given bar easily. 140 DATA 2,12,2,12,2,12,2,11,2,9,2,11 The clef at the beginning of a piece of The total duration of each bar should be 150 DATA 4,12,2,7,4,7,2,7 music is followed by the key signature, if one the same, 12 units in the example used. So, if 160 DATA 2,12,2,12,2,12,2,11,2,9,2,11 is present, then by the time signature. This you transcribe a piece of music and the 170 DATA 4,12,2,7,4,7,2,5 consists of two figures placed one above the rhythm doesn't sound right, check that each 180 DATA 6,4,6,2,12,0 other. Essentially, the upper figure shows bar contains the same number of duration how many beats or pulses there are in each units, and correct any errors if you find them. When you type in and RUN this program, you bar, and the lower figure shows the duration The screen-editing facilities of each computer will be asked to INPUT a number between 1 of each of these beats. So 4/4 indicates that allow you to duplicate DATA statements con- and 50 for the tempo. As with the other there are 4 crochet beats per bar. Again, you taining bars that are repeated, which can save programs, the value that you enter here is not need not fully understand the significance of a lot of time. actually the tempo, but the inverse tempo. this if you are just transcribing sheet music What the computer does is to multiply the into DATA tatements for the music programs, TEMPO relative values for duration of each note by although you might like to use it as a guideline The duration values give the relative duration this tempo value—so, a small number gives for choosing the tempo. of the notes, but they don't dictate its tempo, you a fast speed, while a large number gives or absolute speed. When you RUN the you a slow speed. TRANSCRIBING A SIMPLE TUNE program, you will be asked to provide a tempo The reason for using inverse tempo is that You can now begin to transcribe a piece of number which controls this: a small number it makes the programs simpler, and shorter. written music into the numbers or letters that will make the tune play fast, a higher number There is an IF ... THEN check to make sure your computer uses to play the tune—both makes it play slower. In fact, the number you you INPUT a reasonable value, in Line 20. for pitch and duration. INPUT is a sort of inverse tempo, since in Line 30 then actually plays the tune. Inside Fig. 6 shows the rhyme, Three Blind Mice, music a large tempo number means a fast a FOR ... NEXT loop, it READS two pieces of written on a musical staff, along with the speed, not a slow one. An inverse tempo is DATA for each note—the computer's pitch numbers and letters which represent the used here as it is easier to program. value, and a relative duration value. Then, it Line 10 lets you INPUT the tempo value: values of 30-50 are about right. The subrout- ine at 3000 initializes the SID chip, and the one at 4000 sets up arrays HQ% and LQ% for the 37 pitches, and fills them with the values for the high and low bytes which have to be PO KEd into the SID chip. The loop from 100 to 160 is responsible for READing and inter- preting the DATA statements containing the music information at 10000 onwards. Line 100 reads the current pair of pitch and duration values into variables P and D. Line 120 switches on the envelope for voice 1, and POKES the values for the specified pitch into the SID chip (variables SE, EN, SL and SI are used for speed: they are initialized in the subroutine at 3000). Line 110 tests the pitch and bypasses this line if the pitch is 0, BEEPS before READing the next items of DATA. 3050 POKE SI +24,4 signifying the note is a rest. When you use the routine for your own 3060 RETURN Line 130 is a delay loop which gives the tunes, you can change the numbers in the FOR 4000 DIM HQ%(37), LQ%(37) length of the note: the delay depends on the ... NEXT loop so that it READS the correct 4010 TMP=2227:P2=21(1/12) tempo and the duration value. Line 140 number of items of DATA. At the moment, the 4020 FOR 1=1 TO 37 switches the envelope off, and Line 150 is FOR ... NEXT loop has a STEP of 0 so it never 4030 LQ%(I)=TMP-256'INT(TMP/256): another delay loop to give the 'breaks' be- reaches the end of the loop and only stops HQ%(I) =TMP/256 tween notes. The 'off ' time given is a third of when the DATA has run out, with an E out of 4040 TMP=TMP*132 the length of the 'on' time. If the first value in DATA message. 4050 NEXT: RETURN this FOR ... NEXT loop is altered, the ratio of 10000 DATA 17,6,15,6,13,12 `on' to 'off' time can be altered, making the 10002 DATA 17,6,15,6,13,12 notes more separate if the off time is length- 10 INPUT "TEMPO(30-50)";TP 10004 DATA 20,6,18,4,18,2,17,12 ened or flow together more if the off time is 20 GOSUB 3000 10006 DATA 20,6,18,4,18,2,17,10,20,2 shortened. 30 GOSUB 4000 10008 DATA 25,4,25,2,24,2,22,2,24,2,25, The upper limit of both FOR . . . NEXT loops 100 READ P,D 4,20,2,20,4,20,2 should be derived from D'TP to ensure that 110 IF P=0 THEN 130 10010 DATA 25,2,25,2,25,2,24,2,22,2,24, both the 'on' and `off' times are related to the 120 POKE SE,EN: POKE SL,HQ%(P): POKE 2,25,4,20,2,20,2,20,2,20,2 tempo and the duration parameter. The at- SI,LQ%(P) 10012 DATA 25,4,25,2,24,2,22,2,24,2,25, tack, decay, sustain and release values set in 130 FOR DL=1 TO D'TP: NEXT 2,20,2,20,2,20,4,18,2 Lines 3030 and 3040 also affect the 'shape' of 140 POKE SE,EF 10014 DATA 17,6,15,6,13,12 the notes which controls the quality of the 150 FOR DL=1 TO D'TP/3: NEXT sound. 160 GOTO 100 This program uses pitch values from 1 to 37, 3000 SI = 54272 and then changes them into SID chip values CKI 3010 SL=SI +1: SE=SI + 4: EN = 33: in the subroutines starting at Lines 3000 and 10 INPUT "TEMPO(30 —60)"; TP EF =32 4000. You could, if you wished, just use the 20 GOSUB 4000 3020 FOR I =SI TO SI +28: POKE 1,0:NEXT I correct DATA to start with and then miss out 30 RV =36874:K0 = 0:K1=1 3030 POKE SI +5,16'1 +9 the calculation. This is, however, slightly 40 POKE 36878,4 3040 POKE SI +6,1615+ 9 more difficult to work out. 100 READ P,D 5 Note symbol European name American name Rest symbol Relative duration Duration if dotted
CI■ Semibreve Whole note 70- 16 24 J Minim Half note AM_ 8 12 Crotchet Quarter note 4 6 dJ Quaver Eighth note 2 3 iii 47
Semiquaver Sixteenth note 1 1.5 iii produces three different notes, each an octave above or below the others. So the three octaves of the range are each handled by a different VIC sound voice. This may seem awkward, but it enables you to produce better tuning than is otherwise possible. The three pitch numbers in the range 1 to 37 are reduced to numbers in the range 1 to 13, and the correct pitch value is then taken from the array TA% and POKEd into one of the three sound-controlling registers. Lines 120-140 transform the pitch numbers to fall within this range and also select the correct sound-controlling register, whose address is left in the variable RE. (The register for the lowest octave is at 36874, the middle one is at 36875 and the upper one is at 36876). Line 160 contains a delay loop governing the note's `on' time, and Line 180 is a loop controlling its `off' time; the logic is similar to that of the Commodore 64 program above. Line 150 switches the note on by poking the correct value into the chosen VIC sound register, and Line 170 switches it off, after the first delay loop, by setting this register to 0. The variables KO, Kl, RV, RG are used to shorten the time taken to process the main loop, so as to achieve as regular a rhythm as possible.
10 I N PUT"TEM PO (20-30)",TP 20 TP =TP/20 90 ENVELOPE1,1,0,0,0,0,0,0,30, — 2,0, — 5,100,50 95 ENVELOPE2,1,0,0,0,0,0,0, — 127, —127,-127,-127,0,0 100 READ P,D 110 IF P= KO THEN 160 10010 DATA 25,2,25,2,25,2,24,2,22,2,24, 110 IF D*TP > 254 THEN D =254/TP 120 RG = RV 2,25,4,20,2,20,2,20,2,20,2 120 IF P=0 THEN SOUND1,2,0, 130 IF P>13 THEN P=P-12: 10012 DATA 25,4,25,2,24,2,22,2,24,2,25, D'TP:GOTO 100 RG =RG + K1 2,20,2,20,2,20,4,18,2 150 SOUND1,1,49+ P*4,0*TP 140 IF P>13 THEN P=P-12: 10014 DATA 17,6,15,6,13,12 RG =RG + K1 150 POKE RG,TA%(P) As in the Commodore 64 program, the first 160 FOR I= KO TO TrD:NEXT line reads in the tempo value, which should be 170 POKE RG,K0 between 30-60 for the tune given. The 180 FOR I = KO TO TP/3*D:NEXT subroutine at 4000 initializes the array TA% to 190 GOTO 100 hold values to be POKEd into the VIC chip's 4000 DIM TA%(37) sound registers. 4011 FOR 1=1 TO 13: READ The loop from 100 to 190 is responsible V:TA%(I) =255— V: NEXT for READing and interpreting the DATA state- 4020 RETURN ments containing the music information at 4030 DATA 90,85,80,76,72,67,64,60,57, 10000 onwards. Line 100 READS the curren 54,51,48,45 pitch and duration values into variables P an 10000 DATA 17,6,15,6,13,12 D. Line 110 tests for a rest, and bypasse 10002 DATA 17,6,15,6,13,12 Lines 120-150, which handle the VIC chip 10004 DATA 20,6,18,4,18,2,17,12 values, if it detects one. 10006 DATA 20,6,18,4,18,2,17,10,20,2 To obtain the 3 octave range, all three 10008 DATA 25,4,25,2,24,2,22,2,24,2,25, sound voices of the VIC chip are used: the 4,20,2,20,4,20,2 same number POKEd into the three registers , 200 GOTO 100 by the queuing system. The Dragon and Tandy program begins by 10000 DATA 17,6,15,6,13,12 Line 100 reads in the current pitch and letting you INPUT a value which the program 10002 DATA 17,6,15,6,13,12 duration pair. Line 110 tests for a rest. If one uses to determine the speed of the tune, its 10004 DATA 20,6,18,4,18,2,17,12 is called for, it executes a rest of the required tempo. Line 20 checks to see whether the 10006 DATA 20,6,18,4,18,2,17,10,20,2 duration (D times tempo) using the 'null' value you INPUT is less than 1, which is too 10008 DATA 25,4,25,2,24,2,22,2,24,2,25,4, envelope so no sound is made, and returns to small, and if it is, the computer returns to 20,2,20,4,20,2 Line 100. Line 150 plays an ordinary note. Line 10 for you to enter a new value. 10010 DATA 25,2,25,2,25,2,24,2,22,2,24,2, The expression 53 + (P —1)'4 converts the Line 30 READS two variables—one for the 25,4,20,2,20,2,20,2,20,2 pitch numbers 1-37 into the form expected by pitch (the letter) and one for the duration of 10012 DATA 25,4,25,2,24,2,22,2,24,2,25,2, the SOUND command: 1 is converted into 53, the note. To enter sharps add a plus or hash 20,2,20,2,20,4,18,2 2 into 57, 3 into 61, and so on. sign, and for flats a minus sign, after the note. 10014 DATA 17,6,15,6,13,12 If you prefer, you need not perform this Then, in Line 40, the computer plays the calculation on the DATA—by using the con- note, using the PLAY command. The T, in The first line lets you INPUT the tempo; a version table of pitch values earlier in this quotes, indicates that the next string in the value 20 to 30 is about right for the tune given. article, you could use the correct DATA to start line is a number between 1 and 255 (not 155 as Line 90 sets up ENVELOPE number 1, with, instead. indicated in the Dragon manual), which sets which the program uses for playing notes; it the actual tempo of the tune. The value you has an attack segment (attack rate is 30), a MIA INPUT at the beginning of the program is decay segment (decay rate is — 2), a sustain 10 INPUT"TEMPO (1 — 50)1=1";TP inverted, and then converted into a string by segment (where the volume remains steady) 20 IF TP<1 THEN 10 the function STR$. and a final release segment (release rate is 30 READ A$,D The "03" after this in the same line sets the —5). The peak volume is 100 units, and the 40 PLAY"T" + STR$(1NT(1 + 255/ computer to octave 3, while the last part of the sustain volume is 50 units. These values are (TM))) + "03" +A$ line ( + A$) sets the pitch of the note. provided by the last 6 parameters of the 50 GOTO 30 Once the computer has PLAYed the note, it ENVELOPE command. Don't worry if you 1000 DATA E,6,D,6,C,12 goes back to Line 30, to READ the next note's don't understand how the ENVELOPE com- 1010 DATA E,6,D,6,C,12 DATA—unless, of course, the tune is over, in mand works, there'll be more on this in a later 1020 DATA G,6,F,4,F,2,E,12 which case there will be no more DATA, and so article. 1030 DATA G,6, F,4, F,2, E,12 the computer stops with an error message, as Line 95 sets up ENVELOPE 2, which is used 1040 DATA 04C,4,04C,2,B,2,A,2,B,2, explained earlier in the article. when the program is instructed to 'play' a 04C,4,G,2,G,4,G,2 rest. It's a kind of 'null' envelope, which 1050 DATA 04C,2,04C,2,04C,2,B,2,A, doesn't actually let any sound through. The 2,B,2,04C,2,G,2,G,2,G,2,G,2 reason the program uses an ENVELOPE and a 1060 DATA 04C,4,04C,2,B,2,A,2,B,2 SOUND command to play a rest is so that the 04C,2,G,2,G,2,G,4,F,2 timing, whether of notes or of rests, is all 1070 DATA E,12,D,12,C,12 taken care of by the system of queuing notes. The rate at which notes are played is not governed by the execution time of the programs, but by the computer's internal queuing system. If you tried to produce rests with delay loops, the queuing system would handle all the notes and feed them out to the sound chip, but the delay loops would occur out of sequence and would effectively be lost. So the program uses a SOUND command both for notes which sound and for rests and the two kinds of event are then handled similarly Here we look at how you can make small improvements to standard sort routines to increase their speed. And give details of one routine that beats the lot hands down!
All techniques used for sorting data into a the second row, value 72 is identified as the 130 NEXT Z predefined order come to grief because of highest incorrectly placed value, exchanging 140 GOTO 10 time or memory restrictions. Some sort of with 11 by the third row. 3999 REM DELAYED REPLACEMENT SORT compromise has to be established so that the 4000 FOR 1=1 TO AA-1 most efficient sorting method can be used for top bottom 4010 LET K=1 a particular application. No single sorting 67 35 72 19 47 38 11 [86] 4020 FOR J=1+1 TO AA method is ideal for every application. 67 35 [72] 19 47 38 [11] 86 4030 IF A(J)
If your phone bill can stand it, you can dial up already talking about network software and dards for international communications. In the world through your computer and hardware packages which will enable ma- many spheres, such as computers, this effec- modem. On a more homely level, you can link chines using the same operating system to tively means that standards are set for inter- up to fellow enthusiasts and join one of the upload and download software directly—no nal, domestic communications, too. This is booming areas of home computing— matter how different the machines. welcome news for computer owners who communication via bulletin boards. The empty bulletin board upon which consequently have the opportunity of com- A bulletin board is, at its simplest, just notices are pinned is the memory of a com- municating with other owners throughout what it sounds like—the electronic equivalent puter or, more usually, the computer's Europe. In the UK, modems must also be of a club's notice board on which anyone can storage system. Obviously the storage system pin notices to be read by other members of the for a BB of any size must be at least a floppy club. All you need to read what's on these disk drive. Anything smaller would simply be bulletin boards and to write your own notices too small and would also probably be much is a modem (see pages 618 to 621), some too slow. relatively simple terminal software, a tele- Anyone who has the correct equipment and phone and, of course, the telephone number software, knows the telephone number and, in of a bulletin board. Access to bulletin boards some cases, the right password can read is now relatively cheap—often the cost of a what's on the bulletin board and can write local phone call alone—and many modems are their own notices. What those who use a coming onto the market at very attractive bulletin board are doing is reading from or prices. writing to another computer's memory or Although bulletin boards, or `BBs' as they storage system. are commonly known, have been around for a Most of the BBs springing up around the couple of years—especially in the USA—it's country have been set up by volunteers. In the only recently that they have become popular tradition of grassroots computing, BBs are in the UK. But there's every indication that usually free—although there are those who BBs are set to mushroom. Already they are charge a subscription. One of the problems, of growing at the rate of several a month. course, is keeping non-members out. The usual security is a password, but if the huge UP LO ADING/DOVVNLOADING mainframe computers of the US Defence Computer owners with something in Department cannot keep 'hackers' out then common—the same model of computer, for what chance has a small club of keeping out instance, or simply an interest in computer unwanted intruders. In fact, most BBs wel- communications—can communicate with come intruders! each other over long distances. BBs are not just used as simple notice boards. It is STANDARDS possible to upload and download software via Distance is no object, of course. One com- a bulletin board. Many people are excited puter can communicate with another com- about the prospects for making superficially puter anywhere else in the world as long as incompatible computers much more compat- they are using compatible modems. With the ible by using these methods. right equipment it is possible to gain access to The principle behind this particular idea is more than a thousand BBs in the USA and that all characters are converted to their Canada. Unfortunately you will need special ASCII codes which are, of course, standard to equipment to get through to North America, the majority of computers. These in turn are since manufacturers do not conform to the converted into binary analogue signals. European CCITT standard for modems. In rather the same way that the dots and CCITT is usually known in English as the dashes of Morse Code represent the same Consultative Committee on International characters in any language so the 'modulated' Telegraphy and Telephony but the real name signals from a computer represent the same of this United Nations agency is the Comite characters as far as just about every other Consultatif International Telephonique et computer is concerned. In the USA they are Telegraphique. The organization sets stan- USES OF BULLETIN BOARDS FULL OR HALF DUPLEX ABILITY TO UPLOAD AND -WHICH WILL SUIT YOU? DOWNLOAD ACCESS BY MENUS COMMON STANDARDS EXPLORING THE NETWORK BITS AND BAUD SPEEDS TERMINOLOGY USED
passed by the British Approvals Board for of BBs operate at 300 baud which means that Baud rates go up in steps: from 300 to 600, Telecommunications (BABT). they send and receive data at 300 bits per from 600 to 1200, 1200 to 2400 and so on, second—or one bit every 3.3 milliseconds. doubling every step up to 9600 baud. TRANSMISSION SPEED Most commercial systems such as Prestel or On most computers, according to the International and national agencies still leave Micronet send and receive information at CCITT standards for the RS232 interface, plenty of room for manoeuvre on the part of 1200/75 baud. This means that they send the voltages used to represent 0's and 1's are manufacturers. Modems can operate at differ- data at 1200 bits per second, but that the user + 12v and — 12v. But some computers, such ent 'speeds', for example. The vast majority can only transmit data at 75 bits per second. as the Commodore 64, for instance, use + 5v and 0 v and a low cost converter may be necessary. ACCESS BY MENUS Many people are puzzled to discover that one BITS AND BAUD RATES model of computer can apparently under- Each byte is usually made up of a start bit, stand another completely different model. data bits, a parity bit for error checking and After all, computer manufacturers are const- stop bit(s). Although there will be a natural antly being criticized for failing to adopt logical sequence for the bits, it does not really When you're buying a modem, be certain common standards that would make commu- matter how they are arranged—or even how that it is in fact suitable for use with your nicating between computers easier. It some- many there are—as long as both the trans- computer. Additional interfaces may be times seems, for instance, that one computer mitting and receiving computers 'know' and required, as may be leads and terminal is able to send the other computer commands. `agree' beforehand. Both computers must also software. Remember it is illegal to connect This is not really so. Most BBs enable the user be able to receive data at the speed at which it a modem to the public telephone network to find what they are looking for by using is being transmitted and to transmit data at if it has not received official approval, an menus. the baud rate appropriate to the receiver. often long drawn out process which forces Within these menus, you are asked to There is a good reason why the BB baud some manufacturers to anticipate approval choose an option by pressing the appropriate rate should be that much slower than the baud but otherwise does not restrict sales. 'Ap- key or typing in the appropriate word. Super- rate used by the big commercial networks. proval pending' or similar such wording is ficially, this sometimes looks like one com- BBs' resources are obviously much less than a tell-tale sign that the unit is, at present, puter sending a command to another. But all those of a big network company, and the illegal to use. that's happening is that the program in the equipment that's used would not seem out of Bear in mind that no model made up from host computer or in the modem looks for the place in the home of any micro owner. The a kit of parts will ever receive the necessary characters sent by the guest computer. The slower the baud rate, the less chance there is official approval. ASCII code is used to transmit the characters of picking up unwanted signals. At fast baud If you're an absolute newcomer, seek so each one needs no more than seven bits. rates, the slightest crackle could be mistaken advice from a knowledgeable dealer or It should be remembered that you are for a bit. At slower baud rates, the pulse approach the modem manufacturer direct. communicating with just one central com- which indicates each bit can last much longer Also check with fellow enthusiasts what puter. It's really this host computer that does and can be much more well defined. This cuts they are using. Try to avoid the same most of the work. down the chances of errors due to noise and teething problems they had when setting EXPLORING BULLETIN BOARDS reduces the need for sophisticated equipment. up. The biggest of these teething problems Noise can sometimes be a big problem, and will be actually getting used to the proce- The first step towards exploring the new and many are looking forward to the day when dures involved in using a modem and ever growing world of BBs is the purchase of a fibre optic cables become generally available. establishing contact. modem. The vast majority of BBs operate at Fibre optics offer very 'clean' and very fast 300 baud and most in Europe adhere to the channels of communication. CCITT standards. Access to the many BBs in matically answered and a line is then opened North America is only possible through a DUPLEX up between the two computers. special Bell standard modem. Prestel and It's not just the baud rate that varies from one Terminal software falls into two other commercial networks operate on a baud modem to another. A modem can be either categories—dumb and smart. Smart software rate of 1200/75, but there are switchable full duplex or half duplex. Full duplex means will enable you to download software and save modems which offer a number of baud rates. that a modem can send and receive data at the messages from other computers—essential if The second step will be to purchase or same time, while half duplex means that a you want to operate a bulletin board—while write the terminal software necessary for your modem can only send or transmit at any one dumb software lets you communicate with a computer to send and receive ASCII codes time—never both. BB but does not enable you to save software through a serial interface. The software usu- Half duplex is fine most of the time for or messages from the BB. ally comes with the modem, but be careful home users, and may even be suitable for The central function of the program that over your choice of dumb or smart software. some business users. Unfortunately, mistakes enables your micro to act as a terminal is to The third step is to find out the telephone can be time consuming and irritating. If you send any characters that are typed on the numbers and technical details of BBs. These have asked the host computer to send you keyboard to the appropriate port on the are printed in many of the computer maga- something, once it starts to transmit the data computer and so send data received through zines. BBs often show the telephone numbers you must wait until the end of the trans- the same port to the screen. Each computer is of other BBs and there is an organization mission before being able to send a message to told, by this communications program, how called AFPAS—Association of Free Public the host computer to say you have made a to send data out and what to do with data Access Systems. mistake! This can be very inconvenient for a coming in. After running the terminal software you business user. This sort of software is relatively simple, will be able to call up and communicate with a BBs have been made possible by increasing and even the sort of software that enables such bulletin board. If your modem has an auto- sophistication in communications hardware functions as auto-answer is not particularly dial facility you will probably be connected and software. The big step forward as far as complex. In this instance, the program would automatically. If not you must dial the num- BBs are concerned was the introduction of simply look for an incoming message in the ber yourself, listen for the carrier tone and auto-answering facilities on modems. Calls same way that other programs might look for then place the handset in the rubber cups on made to the bulletin board number are auto- a keypress. the modem in the case of an acoustic coupler or, in the case of a direct-connect modem, flick the appropriate switch. Note that some BBs require you to dial the number, let the phone ring once and then redial. This is so that the appropriate connec- tion can be made. Most BBs operate in a very similar way, so the procedure is roughly the same for each one. You should first of all see a greeting and a request for information displayed on your screen. This is the stage at which passwords and identification numbers are needed if the BB is one that requires a subscription. Some such BBs will not simply dismiss you. They may have special facilities for guests, inform- ation about the service and a limited amount of time and space on a special BB. Free BBs will usually ask you for your name and home town and some technical specifications of your computer, the screen size, for example. The technical details are necessary to enable the host to set up the system to function properly with your Like most viewdata services BBs are menu CEEFAX, run by the BBC, and ORACLE, computer. driven. Calling up one of the optiotis on the run by the independent television companies. You will then be given some technical main menu will probably lead you to another information—the times during which the BB menu, which may in turn lead you to another Viewdata—A similar service to Teletext but is available and a time limit for your call, menu, and so on until you eventually arrive at with two way communication possible. Pre- perhaps. It is important to take note of the the option you require. Many BBs have a 'new stel is an example of a Viewdata service. times during which the BB operates, because user' section and that will be indicated on the Communication is usually, though not neces- many are run on a purely voluntary basis and main menu. The 'new user' section enables sarily, as many people think, by way of calling outside those times—especially in the you to register with the BB. You are asked for telephone lines. middle of the night—might cause a lot of your name and address and you can choose a inconvenience. password for use in future calls. Other options Videotex—This is a generic term used to may include a technical information section, a describe all forms of computer generated `Utilities' section which tells you the duration information services and covers both Teletext of your call so far and displays information and Viewdata. about other services. Bulletin boards also fall under the generic The heart of the BB is the actual bulletin heading of Videotex as they are really a form Is there any way I can protect 1.11 board itself, which contains public notices of Viewdata. Some confusion arises because messages I have left on a bulletin which other people have put there for anyone BBs have begun to develop and grow into board? to read. Often there is also a section for private something more than simple boards on which The answer is, in theory, yes, in practice messages. This really consists of smaller BBs notices can be written and read. Some of them usually not. In some instances it is very to which access is limited by a password. offer an information service. easy to bypass preliminary password Individuals can leave messages for other controls. individuals, or groups can form their own Network—Strictly speaking, this refers to The very nature of a bulletin board is bulletin board within the main bulletin board. the direct linking up of a number of com- that it is open to public inspection—it is, puters in a limited group for a specific in effect, a notice board which, almost TERMINOLOGY purpose usually in a business or research by definition, means that information There are many technical terms used in environment. The main distinction between a placed on it is intended for public computer communications which are not network and other forms of computer com- scrutiny. But writing to it usually does used very often in other branches of comput- munication is that a network involves direct mean password acceptance. ing. This sometimes leads to confusion about connections between computers and/or peri- Some bulletin boards delve into areas the meaning of some terms. Here is an pherals. The purposes of networking com- which perhaps may be more closely explanation of some of those terms which are puters is so that they can share facilities such linked to electronic mail—essentially likely to lead to confusion. as databases or printers rather than pool private communications between resources. individuals at personal or business Teletext—Information services which in- The meaning of the word network is, level. Here, the use of passwords volve broadcasting pages of information and however, gradually being degraded and it is very much the norm. Try displaying them using the 'spare' lines on a now sometimes refers to any grouping of to choose a novel password. television set. The communication is one way computers even if the connection between only and users cannot transmit. Examples are them is a central computer as in Viewdata. This flight simulation program is similar to those used in flying schools to teach pilots how to fly using their instruments alone: the first part reproduces the cockpit
Games programs vary from sheer fantasy, the controls when the aeroplane is 2000 which involves you entering an imaginary metres in the air and 20,000 metres away world and taking part in an adventure, to from the target runway. Through the cockpit simulations of real-life situations. These allow window you can see little—just the horizon, you to test your capabilities in a potentially when it is in view, and the distant dot of the dangerous situation without causing harm to runway—so like a seasoned pilot you must yourself or writing off millions of pounds rely on your expertise at responding to the worth of equipment. instrument panel to bring you and all your Flight simulation programs have an ele- passengers safely in to land. ment of fantasy—alone in the cockpit, all the crew stricken by a mysterious illness, you, THE INSTRUMENTS single-handed, bring the aeroplane in to land. There are four dials on your instrument But sophisticated programs of this type have panel. The first one tells you your airspeed. real practical use—so much so that most This varies according to whether you are major airline companies and flying schools diving (your speed increases), climbing (your use them regularly. speed falls off) and changing engine power. A counter underneath the airspeed dial tells you TRAINING SIMULATORS your compass bearing. At the top end of the scale there is total The second dial shows you where the simulation—Phase 3' in the jargon of the horizon is in relation to your aeroplane. This Federal Aviation Administration (America's means that even when the horizon is not in civil aviation governing body), which allows view through the cockpit window, you still you to experience everything that the pilot in know where it is. The counter underneath a real aeroplane does. You see what he sees this dial gives you the bearing of the runway. through the cockpit window (including a The third dial gives you an altitude read- slightly differently angled view for the co- ing. This has two hands, one for thousands, pilot); you feel what he feels on take-off and and the other for hundreds. The counter landing, and during turbulence; and you hear underneath calculates the drift of the what he hears, including air traffic control aeroplane—as the runway is 100 metres wide, commands. Theoretically, a pilot can com- a drift of over + 50 or — 50 will cause you to plete all his training in one of these, and miss it altogether. obtain his licence without once leaving the The last dial tells you the engine speed in ground. revolutions per minute. The counter beneath lets you know the distance you are from the TABLE-TOP SIMULATORS centre of the runway. At the other end of the scale, the flight simulation programs are very similar to the LANDING THE AEROPLANE one that follows. In the case of the Dragon and Tandy, the Table-top units that can be 'flown' in the picture through the cockpit window becomes classroom are good for teaching cockpit pro- cleaner as you approach your destination—you cedure, and developing the reflex speeds of can see the runway as you guide your aeroplane the pilot. towards it. With the other computers you must They are essential for learning instrument centre the radar image of the runway. flying, a technique that allows the pilot to When you assume the controls, weather navigate solely by referring to the instrument conditions are fair, and the runway is due panel—something that every pilot has to do north. Landing like this is not hard, and the when the weather conditions are bad. game would quickly lose its fun if you could not vary this. To add difficulty, you can WHAT THE PROGRAM INVOLVES specify the speed and direction of the wind: The flight simulation program in this three for instance, a howling gale from the side will part article assumes that you have taken over make your job very much harder. EXPLAINING FLIGHT THE INSTRUMENT PANEL SIMULATION RECREATING AIRCRAFT TRAINING PROGRAMS MOVEMENT LEARNING TO LAND STALLING THE AIRCRAFT INSTRUMENT FLYING A FLYING SCHOOL AT HOME written for Simons' BASIC, including this MOVING THE AEROPLANE DRAWING THE COCKPIT one. The only minor modification you will The range of controls you have closely approx- To draw your cockpit, enter the first part of have to make is to preface each graphics imates to the controls of the aeroplane— the program into your computer. command with a @. though you are pressing keys, rather than using a joystick. a 5100 A$ = "AIRSPEED ❑ HORIZON ❑ In a real aeroplane, to control pitch—the 1 POKE 23658,8 ALTITUDE LI ❑ RPM" up and down movement—the joystick is 110 GOTO 5000 5110 B$="BEARING ❑ RUNWAY ❑ moved backwards or forwards, thereby mov- 5000 LET PP= —1: LET RR= —1 DRIFT 0 DISTANCE" ing the elevators on the tailplane upwards or 5010 LET C= PI/180: LET PY= —20000: 5120 HIRES 0,1:MULTI 4,0,5: downwards. You will be using two keys to LET PZ = 2000: LET AS=150 COLOUR 0,1 create the same effect, and in the third section 5110 PLOT 10,175: DRAW 235,0: DRAW 5130 BLOCK 0,110,160,200,2 of the article you will enter the part of the 0, — 90: DRAW — 235,0: DRAW 0,90 5140 TEXT 0,120,A$,3,1,5: program that does this. 5120 FOR K=0 TO 3: CIRCLE TEXT 0,175,B$,1,1,5 The roll of the aeroplane—the side to side 35+K'60,50,20: NEXT K 5150 LINE 0,171,160,171,0: movement—is controlled by moving the joy- 5130 PRINT AT 12,2;"SPEED ❑ El ❑ LINE 0,200,160,200,0 stick from side to side. This moves the HORZN ❑❑ 1] ALT 0 ❑ ❑ 0 RPM" 5160 FOR Z=0 TO 3:CIRCLE 20+Z'40, ailerons—the control surfaces on the wings. 5150 PRINT AT 20,0;"BEARING ❑ ❑ 150,15,15,0 Again you'll be using two keys to turn you RUNWAY 0 ❑ DRI FT 0 0 DISTANCE" 5170 IF Z=1 THEN TEXT 57,146,"E", either to the right or the left. 5170 PLOT 87,50: DRAW 5,0: DRAW 3,-3: 0,1,1:NEXT Z Your last two controls enable you to speed DRAW 3,3: DRAW 5,0 5180 FOR K=0 TO 9:PLOT (20 +Z*40)+ up or slow down the engine, essential for 5180 LET X=35: LET Y=50: GOSUB 7000: 17*SIN(rn/5),150 —19*COS finely timing your landing, or making sure LET X=155: GOSUB 7000: LET X=215: (K*7r/5),0:NEXT K,Z that you do not stall. GOSUB 7000 6900 STOP STALLING SPEED 7000 FOR K=0 TO 2131 STEP PI/5: PLOT Aeroplanes stall when they fall below a certain X+17'SIN K,Y+17*COS K: DRAW 2*SIN speed, which means that they literally drop K,2*COS K: NEXT K: RETURN from the sky. In this program, if your air- speed falls below 30 metres per second, the The POKE in Line 1 sets the computer to aeroplane will start to dive steeply, turning to upper case mode. Lines 5000 and 5010 place one side as it plummets. If you've got enough the aeroplane in its position in the sky: 2000 height, quick action may save you, but a stall metres up in the air, 20,000 metres from its is dreaded by every pilot. destination, motionless; next week you will enter the lines that will make it move. DIVIDING THE PROGRAM Line 5110 draws the cockpit window, and The program is too long and complex to be the dials beneath are drawn by Line 5120, given all at once, and so it has been split into using a FOR ... NEXT loop. The labels for the three parts. dials and counters are printed by Lines 5130 In this first part what you are doing is and 5150. Line 5170 draws a diagrammatic setting up the screen to show the interior of aeroplane in the horizon dial—the artificial the cockpit, with its window, the four dials, horizon will not be drawn until the next part. which are labelled, and the labels for the Line 5180, and the GOSUB routine 7000, set counters. the centres of the dials and draw the in- The commands this involves will be fam- dicators round the three dials that need them: iliar to most of you from other programs. Airspeed, Altitude and RPM, using SIN and Dragon and Tandy users, however, will come COS as explained on page 250. across a command that they may not have had If you RUN the program now, your simu- to use before, PCOPY—unique to these lated cockpit will appear on the screen. computers—which will be explained in detail later. In part two, the section of the program To enable you to access the Commodore 64's entered enables the dials and counters to high resolution graphics, this program is become sensitive to the movement of the written in Simons' BASIC. This means that aeroplane, and a temporary command causes you cannot run it on the standard Commo- the aeroplane to fly randomly, without a pilot dore unless you fit a Simons' BASIC cartrid- at the controls, so that you can watch the ge. But those of you who don't have a instrument panel functioning. The final sec- cartridge shouldn't despair. A machine code tion allows you to take control of the aero- program that allows you to run these plane, and assesses your landing technique so programs will be given soon in INPUT. you can judge your progress. Then you can enter and RUN any program A$ and B$, as defined in Lines 5100 and 30 X =190:GCOL0,3 DRAW 1180,500:DRAW 100,500: 5110, contain the labels for the dials and 40 FOR P = 0 TO 3 DRAW 100,900 counters. Line 5130 draws a black block 50 MOVE X + 100,250 215 MOVE 0,908:DRAW 1276,908: underneath the cockpit window, to contrast 60 FOR T = 0 TO 2'P1+.3 STEP .3 DRAW 1276,1020: DRAW 0,1020: the dark interior of the aeroplane with the 70 DRAW X +100*COS(T), DRAW 0,908 light blue window. Line 5140 positions the 250 + 100*SIN (T) 220 VDU 5:MOVE46,400:PRINT labels, and Line 5150 draws two lines to 80 NEXT "AIR SPEED" suggest that the labelled counters are set in a 90 X=X+300 230 M OVE410,400: PR I NT" H OR IZ" separate panel from the dials. Line 5160 100 NEXT 240 MOVE742,400:PRINT"ALT" draws the circles for the dials (actually some- 110 X=170 250 M0VE1042,400:PRINT"RPM" what elliptical because of the way the graphics 120 FOR P = 0 T03 260 MOVE78,100:PRINT"BEARING" screen works), and the diagram of an aero- 130 X=190 + P.300 270 M0VE396,100: PR I NT"RUNWAY" plane in the horizon dial. Line 5180 draws the 140 FOR T=0 TO PI*2 STEP PI/5 280 M OVE710,100: PR I NT" D R I FT" indicators around the other three dials. 150 MOVE X + 100*SIN(T), 290 M OVE1026,100: PR I NT" D 1ST" So far, this program will show you a 250 + 100*COS(T) 300 VDU4:GCOL3,3:ENDPROC simulated flight deck. In the next part you 160 DRAW X + 90*SIN(T), will enter the part of the program that enables 250 + 90*COS(T) Lines 30 to 100 draw the control dials, using a your aeroplane to fly. Line 5190 must be 170 NEXT FOR ... NEXT loop. Lines 110 to 190 draw the deleted before adding this next section. 180 IF P=0 THEN P=P+1 ten indicators round three of the dials— 190 NEXT Altitude, Airspeed and RPM—the third dial, 200 MOVE 420,260:DRAW470,260: which displays the artificial horizon, does not 10 MODE1 DRAW490,230:DRAW510,260: need the indicators. The diagrammatic aero- 15 PROCSCREEN: END D RAW560,260 plane, which appears in the horizon screen, is 20 DEF PROCSCREEN 210 MOVE 100,900:DRAW 1180,900: drawn by the Line 200. The artificial horizon The instrument panel on the Commodore Flight Simulator ... and how it appears on the Acorn Flight Simulator itself will not be drawn until the second part DRAWN U$(VAL(B$)):G0T04050 Lines 20 to 110 set up the arrays for of the program is entered. 4030 IF B$ = " ❑ " THENN = 0 ELSEN = ASC writing on the graphics screen, as explained in Line 210 draws the cockpit window, and (B$) — 64 detail on page 192, and this is carried out by the remaining lines label all the dials and 4040 DRAW LE$(N) the printing subroutine contained in Lines counters. 4050 NEXT:RETURN 4000 to 4050. RUNning the program at this stage will 5000 PP= —1:RR = —1 Lines 5000 and 5010 position the aero- show you the interior of the cockpit, but the 5010 PI = 4*ATN(1):C = PI/180: plane in the sky: 20,000 metres from the aeroplane can't fly, and neither can you PY = — 20000:PZ =2000:AS =150 centre of the runway, at a level of 2000 control it yet. 5110 PCLS:LINE(10,0) — (245,80),PSET,B metres, though at this stage it is motionless— 5120 FORK = OT03:CIRCLE(35 + K*60, it won't fly until you enter the lines in part 120),25,5:NEXT two of the program. 10 PCLEAR8:PMODE4,1 5130 DRAW"BM18,88S4":A$ = "AIRSPEED": The cockpit window is drawn by Line 20 DIM LE$(26) GOSUB4000:DRAW"BM80,88": 5110. The next line, 5120, draws the circles 30 FOR K = 0 TO 26:READ LE$(K):NEXT A$ ="HORIZON":GOSUB4000 for the dials, and Lines 5130 to 5160 label 40 FOR K = 0 TO 9:READ NU$(K):NEXT 5140 DRAW"BM140,88":A$ = "ALTITUDE": the dials. Line 5170 draws a diagram of the 50 DATA BR2,ND4R3D2NL3ND2BE2, GOSUB4000:DRAW"BM208,88": aeroplane on the horizon dial. The indicators ND4R3DGNL2FDNL3BU4BR2, A$ = "RPM":GOSUB4000 on the dials are drawn by Line 5180, and the NR3D4R3BU4BR2,ND4R2FD2GL2BE4BR, 5150 DRAW" BM18,160":A$ = "BEARING": subroutine in Line 7000. NR3D2NR2D2R3BU4BR2 GOSUB4000:DRAW"BM82,152": The PCOPY commands in Line 5190 draw 60 DATA NR3D2NR2D2BE4BR,NR3D4R3U2 A$ ="RUNWAY":GOSUB4000: the graphics onto unseen pages, and then LBE2BR,D4BR3U2NL3U2BR2,ND4BR2, DRAW"BM80,160":A$ = "BEARING": copy them onto the screen. This aids back- BD4REU3L2R3BR2,D2ND2NF2E2BR2 GOSUB4000 ground preservation—the background is re- 70 DATA D4R3BU4BR2,ND4FREND4BR2, 5160 DRAW"BM144,160":A$ = "DRIFT": newed invisibly, and then transferred com- ND4F3DU4BR2,NR3D4R3U4BR2, GOSUB4000:DRAW"BM200,160": plete to the screen, so that there is no time lag ND4R3D2NL3BE2,NR3D4R3NHU4BR2 A$= "DISTANCE":GOSUB4000 when the background is updated. This means 80 DATA ND4R3D2L2F2BU4BR2,BD4R3U2 5170 DRAW"BM81,118R9F5E5R9" that when the aeroplane is flying and the dials L3U2R3BR2,RND4RBR2,D4R2U4BR2, 5180 X = 35:Y =120:GOSUB7000:X =155: move, they can all do so simultaneously— D3FEU3BR2,D4EFU4BR2 GOSUB7000:X =215:GOSUB7000 without PCOPY only one dial would move at a 90 DATA DF2DBL2UE2UBR2,DFND2EUBR2, 5190 PCOPY3T05:PCOPY3T07:PCOPY4T06: time. R3G3DR3BU4BR2 PCOPY4T08:SCREEN1,1 RUN the program so far, and the cockpit 100 DATA NR2D4R2U4BR2,BDEND4BR2, 5500 GOTO 5500 will appear on your screen. R2D2L2D2R2BU4BR2,NR2BD2NR2BD2 7000 FORK = OT09:LINE(X + 24*SIN(K*131/5), In the next part you will enter the com- R2U4BR2,D2R2D2U4BR2,NR2D2R2 Y-24TOS(K*P1/5)) — (X +21*SIN mands that enable the aeroplane to fly, D2L2BE4,D4R2U2L2BE2BR2, (K*PI/5),Y— 21*COS(K*PI/5)),PSET: though, at that stage you will have no control R2ND4BR2,NR2D4R2U2NL2U2BR2, NEXT:RETURN over it. The aeroplane will be under the NR2D2R2D2U4BR2 control of a manic autopilot, causing it to dive 110 GOTO 5000 The first part of this flight simulator program and climb randomly. The third part of the 4000 FORK =1TOLEN(A$) includes a command not so far dealt with in article will install the pilot's controls and you 4010 B$ = M1D$(A$,K,1) INPUT—PCOPY, which makes sure the will finally have the passengers' lives in your 4020 IF B$> ="0"ANDB$ < = "9" THEN screen image moves smoothly. hands. DESIGNING THE CHARACTERS STORING UDGS IN A BANK SAVEING UDGS ON TAPE OR DISK CONTROL KEYS
million million options—you will want to be able to keep it. So the program lets you store a bank of completed UDGs that you can call back when you want them. You can SAVE the UDGs out of the program and onto tape, and you can then LOAD them back into any program for use on screen—or back into the UDG generator for further editing. The program is in two parts. The first part of the listing, which follows, allows you to create the basic UDG generator. It sets up a grid on screen, and allows you to move around the display to plot the pattern of pixels you want in the finished UDG. In the following part of the article, you will add the routines which enable you to modify the UDG in more subtle ways, and to display it. You can save having to type it in again next time by SAVEing it on tape when you have entered it. a When you type in the program and RUN it, you will see a square 8 x 8 grid in the middle of the screen. This is the 'graph paper' on which you are going to plan your UDG. So you can select which squares to block in, this sets a pixel. You have a cursor, which takes the form of a white square. This square is not printed in a special colour, but is the BRIGHT version of whatever it overprints. This is so you can see it, whether or not the background square has been set. The program is written so that you If you're fed up with laboriously takes a long time to see the results. move the cursor with the cursor keys and working out UDGs on paper, then So here's a program to change all that. It press 0 to set, or reset, the pixel. type in this program and take a rest replaces the piece of squared paper with a neat If you want to change these keys to a more screen display which lets you plot in pixels personally convenient set, simply change the while the machine does the work where you want them. Instead of you having characters inside the IF 1$ = . .. statements in and you plot the shape you want to work out the DATA values by hand, it tots Lines 6520 to 6555 to those of the keys you them up automatically. wish to use. But the real strength of the program is that You can use this method to set the program UDGs are one of the most versatile tools it also lets you see the UDG as it builds up— up for use with some joystick interfaces, but if available to the graphics programmer—and life size—and you don't have to bother about you have a Kempston-compatible interface, they have been exploited in numerous POKEing the DATA into another program. you will need to change these lines even more. programs in INPUT. But one of the draw- Various control options let you adapt the Instead of the I N KEY$ in Line 6510, you need backs, if you want to design your own, is the UDG at the touch of a button—perhaps you to use IN, as pages 464 to 469 explain. effort that goes into first plotting them on would like to see the inverse, or turn it round Whichever keys you decide to use, you paper, then working out the DATA, and finally from left to right. should be careful not to use the same keys as POKEing into memory so you can display When you've created the UDG you're the control keys. This part of the program them on screen. And if you've got it wrong, it looking for—and you have nearly 20 million only uses three control keys (these are ex- plained further on in the article) but the next UDG you want to pick up. After pressing the 30 LET X=11: LET Y=8: LET NX= X: LET part will use more. Altogether, C, I, M, P, R, appropriate key, the UDGs you want will NY =Y S and T are reserved. appear in the grid. 100 LET A$="": FOR N=144 TO 164: LET Using either the keyboard or a joystick, the A$ = A$+ CHR$ N: NEXT N cursor can move around inside the grid in the SAVEING UDGs ON TAPE 110 LET B$="": FOR N=65 TO 85: LET middle of the screen. If you press 'fire', key 0 Although the UDG editor is fine as it is, you B$=B$+CHR$ N: NEXT N on the keyboard, then you will see the colour need to be able to SAVE your finished designs 1000 FOR N=87 TO 151 STEP 8: PLOT N,48: of the cursor change to indicate that the pixel to tape for use in your own programs. To DRAW 0,64: NEXT N `underneath' the cursor is now on. If you match this, there is a LOAD option so you can 1010 FOR N=48 TO 112 STEP 8: PLOT 87,N: move the cursor away from that position, you LOAD previously SAVEd UDGs for re-editing. DRAW 64,0: NEXT N will see that the square is now shaded in. You can use either the SAVE or the LOAD 2000 PRINT AT 3,5;A$ Carry on in this way to build up your design. facility by pressing the T key. You will be 2010 PRINT INVERSE 1;AT 2,5;B$ The program has a number of options asked whether you wish to SAVE or LOAD, and 2400 GOSUB 6500 which you can access at any time while editing then the computer will do this. When you 2500 IF INKEY$="P" THEN GOTO 5000 a UDG. The first of these is to store the SAVE to tape, the bytes of the 21 UDGs 2510 IF INKEY$="S" THEN GOTO 5100 UDG. To get this option, simply press key currently stored are SAVEd as a block of 2520 IF INKEY$="T" THEN GOTO 5200 S—this is the first of the control keys men- memory—so don't forget to store the UDG 3900 GOTO 2000 tioned earlier. you are working on before SAVEing the bank. 5000 INPUT "WHICH CHARACTER (A— U)?", You will then be asked what position in the LINE C$ The final part of this article will give you 5010 IF C$
77 " 300 GOTO 130 1520 A = ASC(A$) -64:RETURN 40 A$ = "ABCDEFGHIJKLMNOPQRSTUVW 1200 GOSUB 1500 1600 GOSUB 1500 XYZ" 1235 FOR Z=0 TO 7:T=0:FOR ZZ=0 TO7 1610 FOR ZZ=0 T07 50 X = 0:Y = 0:Z(0) =128:Z(1) =64: 1240 C1 =1396 +ZZ+Z*40:C2= PEEK(C1) 1611 AA= PEEK(12288+ A*8 + ZZ) Z(2) = 32:Z(3)=16:Z(4) = 8: 1250 IF C2=230 THEN T=T+Z(ZZ) 1612 FOR Z1=0 TO 7 Z(5) = 4:Z(6) = 2:Z(7) =1 1260 NEXT ZZ:POKE 12288 + (A*8) +Z,T: 1614 IF AA -Z(Z1) = >0 THEN AA= 100 PRINT "Eggggigggigggigg POKE 12288 + Z,T AA -Z(Z1):POKE 1396 + Z1 +ZZ*40, gga ";TAB (12);"12345678" 1280 NEXT Z:GOTO 130 230:GOTO 1620 110 FOR Z=1 TO 8:PRINT TAB(10);Z; 1400 POKE 198,0:POKE 53272,21:N$="": 1616 POKE 1396+Z1 + Z1.40,207 "11.2EFFEEEEE INPUT "DENIER NAME";N$:IF N$=`' 1620 NEXT Z1,ZZ:GOTO 130 NEXT THEN 30 120 PRINT TAB(12);"a= 1405 PRINT "A(S)AVE OR (L)OAD?":0U =0 ❑❑❑❑❑❑ ":PRINT "a"; 1406 GET K$:IF K$="S" THEN 10 PRINT CHR$(8):POKE 51,255: TAB(7);A$:PRINT TAB(7); OU=1:GOTO 1410 POKE 52,27:POKE 55,255: POKE 56,27:CLR 122 FOR Z=1 TO 26:PRINT"al -";: 1407 IF K$< >"L" THEN 1406 20 FOR Z=0 TO 511:POKE 7168+Z, NEXT Z:PRINT:PRINT TAB(7);A$ 1410 PRINT "0":R$=CHR$(13):OPEN PEEK(32768+Z):NEXT Z 130 XX = X:YY = Y:C =1396 + X +Y .40: 1,1,OU,N$:REM DISK:- OPEN 30 PRINT "1:1":POKE 36879,25:POKE CC= PEEK(C) 1,8,0U,"©:"+N$ 36869,255 140 POKE C,233:P=PEEK(197):POKE 198,0 1413 FOR Z=12296 TO 12504:IF OU=1 33 FOR Z=0 TO 7:POKE 7168 +Z,255:NEXT Z 150 IF P=12 AND X>0 THEN X=X-1 THEN Z$=STR$(PEEK(Z)):Z$= 35 PRINT " sip] CHARACTER ❑ ❑ 155 IF P=23 AND X<7 THEN X=X+1 RIGHT$(Z$,LEN(Z$) -1) GENERATOR" 160 IF P=50 AND Y>0 THEN Y=Y-1 1414 IF OU=1 THEN PRINT#1,Z$R$: 38 PRINT "all ❑❑❑❑❑❑❑❑ 165 IF P=55 AND Y<7 THEN Y=Y+1 GOT01420 7777 ❑❑❑❑❑ " 170 IF PEEK(653) = 1 THEN POKE C,230: 1415 INPUT #1,Z$:POKE Z,VAL(Z$) 40 A$ = "ABCDEFGHIJKLMNOPQRSTUV" GOTO 130 1420 NEXT Z:CLOSEl:GOTO 30 50 X= 0:Y=0:Z(0)=128:Z(1)=64: 180 IF PEEK(653) =2 THEN POKE C,207: 1500 PRINT "Iggggggga";TAB(14); Z(2) = 32:Z(3) =16:Z(4) = 8: GOTO 130 "ENTER LETTER":FOR Z=1 TO 25:NEXT Z Z(5) = 4:Z(6) =2:Z(7)=1 100 PRINT "I§Igigggigigingiggal After you have finished a whole bank, or as 0012345678" much of a bank as you want to use, you can 110 FOR Z=1 T08:PRINT z;" 11 When you type in and RUN the Acorn SAVE the bank to tape. This facility means that ❑❑❑❑❑❑❑ E":NEXT program, the computer draws a blank grid you have a permanent record of the UDGs 120 PRINT and a line of characters is PRINTed above it. which you can LOAD back into the computer "aDOCIMM1777171 The grid is the main part of the UDG at any time. The next part of this article will ":PRINT "a"A$:PR1NT A$ generator and represents the 8 x 8 group of explain how you call up the UDG for use in 130 XX =X:YY = Y:C =7880 +X + Y'22: pixels in the UDG. You can move the cursor your own programs. For now, you can LOAD it CC = PEEK(C) around inside it, setting pixels where you back into the program, for later editing. 140 POKE C,233:P=PEEK(197):POKE 198,0 want, to build up your character. You can tell You can use the SAVE facility by pressing 150 IF P=33 AND X>0 THEN X=X-1 when a pixel is set, since a filled-in circle is 'CONTROL! and S together. To LOAD a previ- 155 IF P=26 AND X<7 THEN X=X+1 printed in the grid square to represent a filled- ously SAVEd bank back into memory from the 160 IF P=22 AND Y>0 THEN Y=Y-1 in pixel—but to start with, the grid is blank. program, press !CONTROL! and L together. 165 IF P=30 AND Y<7 THEN Y=Y+1 You can move around with a variety of keys, This half of the program has just one more 170 IF PEEK(653) =1 THEN POKE C,230: depending upon what you want to do. control key availableHCONTROL and E. This GOTO 130 To move and leave the pixels unchanged, ends the program, and returns you to BASIC. 180 IF PEEK(653) = 2 THEN POKE C,207: you can use these keys: P is up; L is down; Z is But next time, you'll see how to add extra GOTO 130 left; and X is right. !RETURN also leaves the facilities, including a print-out routine. 200 POKE C,CC pixels unchanged, and at the same time brings If you use a disk drive, omit Line 20. 250 IF P=8 THEN 1200 you to the start of the next line. 280 IF P=53 THEN 1600 If you press the 'DELETE! key, the pixel 10 *FX11,0 290 IF P=6 THEN 1400 beneath the cursor is set to 0 (or deleted, if it 15 'FX4,1 300 GOTO 130 had previously been set) and the cursor is then 20 *OPT2,1 1200 GOSUB 1500 moved one space to the left. To delete a pixel 25 *OPT1,1 1235 FOR Z=0 TO 7:T = 0:FOR and move the cursor to the right, you can 30 MODE1:DIM A(31),B(31),C(7) ZZ = 0 T07 press the space bar. 40 VDU 23,95,0,0,0,0,0,0,0,255: 1240 C1 =7880+ ZZ + Z*22:C2 = PEEK(C1) The full stop key sets a pixel, and moves FOR T = 0 TO 31:B(T) = T?&COO: 1250 IF C2 = 230 THEN T = T + Z(ZZ) the cursor to the right, while the comma key N EXT:*FX20,0 1260 NEXT ZZ:POKE 7168 + (Ali) + Z,T: sets a pixel and moves the cursor to the left. 50 X = 0:Y = 0:PT = 0: PX = 508: PY = 252: POKE 7168 + Z,T Using a combination of these keys, you can DX = 260:DY = 260 1280 NEXT Z:GOTO 130 quickly and easily move around the grid, 60 PROCASS:VDU23;8202;0;0;0; 1400 POKE 198,0: POKE 36869,240: setting various pixels to create your character. 70 FOR T=0 TO 23:READ T?&C0O:NEXT NS = ":INPUT "DENIER NAME"; As you build up your UDG, you can see its 80 CLS:PROCDISPLAY:REPEAT : N$:IF N$="" THEN 30 actual size from the character above the grid. PROCINST:UNTIL A$ = CHR$(5) 1405 PRINT "gi(S)AVE OR (L)OAD?": This is updated whenever you move. 90 CLS:INPUT""ARE YOU SURE (Y/N)";A$ OU = 0 100 IF A$< >"Y" THEN 80 ELSE END 1406 GET K$:IF K$="S" THEN OU=1: THE UDG STORE 110 DEF PROCGRID GOTO 1410 Once you have finished your design, you can 120 GCOL0,1 1407 IF K$< >"L" THEN 1406 store it in memory in a bank of 32 UDGs. The 130 FOR P = 0 TO 3:MOVE PX — DX*(P = 3), 1410 PRINT "LT:OPEN 1,1,OU,N$:REM current bank (part of the character set) is PY — DY*(P =1):DRAW PX— DX* DISK:— OPEN 1,8,OU,"@:"+ N$ displayed at the top of the screen. It's also (P< >2),PY—DY*(P< >0) 1413 FOR Z = 7176 TO 7352:IF OU=1 THEN possible to call a UDG back from this store 140 MOVE 88 —1040*(P = 3),888 — 48* PRINT#1,PEEK(Z):GOTO 1420 for further editing, if you wish. (P=1):DRAW 88 —1040*(P < >2), 1415 INPUT#1,ZZ:POKE Z,ZZ The up-arrow beneath one of the charac- 888 — 48*( P < > 0):NEXT 1420 NEXT Z:CLOSE1:GOTO 30 ters indicates which position in the bank is 150 GCOL3,3:ENDPROC 1500 PRINT"I§IgigMa ❑❑❑❑❑ currently available. If you store a UDG, the 160 DEF PROCINST ENTER LETTER":FOR Z=1 TO 25:NEXT Z computer puts it in the position pointed to by 170 A$=INKEY$(1):IF A$=" THEN ENDPROI 1505 PRINT"l§giggia ❑❑❑❑❑ the arrow, and if you take a character from the 180 IF A$=";" THEN PROCPOINT(1): ❑❑❑❑❑❑❑❑❑❑❑❑ " bank on to the grid for further editing, you ENDPROC 1510 GET A$:1F A$ < "A" OR A$ > "V" will get the one above the arrow. 190 IF A$ = " — " THEN PROCPOINT( —1): THEN 1500 You need to be able to move the arrow to ENDPROC 1520 A = ASC(A$) — 64:R ETUR N specify which character you want to use. Press 200 IF A$ = CHR$(7) THEN PROCGET: 1600 GOSUB 1500 the semi-colon key to move it to the right. To ENDPROC 1610 FOR ZZ =0 TO7 move left, press the minus-sign key. 210 IF A$= CHR$(1) THEN PROCASIGN: 1611 AA= PEEK(7168 +A*8 +ZZ) When you have positioned the arrow, to ENDPROC 1612 FOR Z1 =0 TO 7 store a character in the bank, press ICONTROLI 220 IF A$= CHR$(12) THEN PROCLOAD: 1614 IF AA —Z(Z1) = >0 THEN AA= and A. To get a character back into the grid END PR OC AA — Z(Z1):POKE 7880+Z1 + ZZ*22, again from the bank, press 'CONTROLS and G. 230 IF A$= CHR$(19) THEN PROCSAVE: 230:GOTO 1620 (A stands for Assign, and G for Get—it is ENDPROC 1616 POKE 7880 + Z1 + ZZ*22,207 often easier to remember the names, rather 290 IF A$ = "," THEN PROCIN:X = X —1: 1620 NEXT Z1,ZZ:GOTO 130 than just the letters.) IF X= —1 THEN Y=Y-1 300 IF A$="." THEN PROCIN:X =X +1: T?(&C00 + PT*8)=A(T+ 24):NEXT IF X=8 THEN Y=Y+1 660 PROCMOVEUDG(0):PROCDISPLAY: 310 IF A$ = "El" THEN PROCDEL:X = X +1: ENDPROC IF X=8 THEN Y=Y+1 670 DEF PROCGET 320 IF A$=CHR$(13) THEN X= 0:Y =Y +1 680 PROCMOVEUDG(1):FOR T=0 TO 7: 330 IF A$=CHR$(127) THEN PROCDEL: A(T + 24) = T?(&C00 + PT'8): N EXT: X=X-1:IF X= —1 THEN Y=Y-1 PROCMOVEUDG(0) 350 X= (X— (A$="X")+(A$="Z")) AND 690 FOR T=0 TO 7:T?(&C00 + 24) = 7: Y= (Y+ (A$="P")— (A$="L")) A(T+24):NEXT:PROCDISPLAY: AND 7 ENDPROC 360 CALL MC:VDU5:MOVE(16+X)'32, 770 DATA 255,255,255,255,255,255, 1023— (16 + Y)'32:VDU224,4 255,255,0,0,0,24,24,0,0,0,0, 370 ENDPROC 60,126,126,126,126,60,0 380 DEF PROCDEL:?(&C18+Y)= 780 DEF PROCASS The Spectrum lets you make UDGs ?(&C18 + Y) AND (255 — 2 A (7 — X)): 790 DIM MC 200:FOR T=0 TO 2 STEP 2: ENDPROC P%= MC The computer then presents you with the 390 DEF PROCIN:?(&C18+Y)= 800 [OPT T editing grid which forms the basis for the ?(&C18 +Y) OR 2 A (7 — X):ENDPROC 810 LDA # 24:STA &70:LDA # 12:STA &71: UDG design. You can move a cursor around 400 DEF PROCNOS LDY #7 inside this grid using the cursor keys and, by 410 CALL MC:VDU5:MOVE(16+X)'32, 820 .M3: JSR PSN:LDA (&70),Y:LDX moving to the pixel you want, you can change 1023— (16 +Y)'32:VDU224,4: #8:.M4:ASL A:PHA:LDA # 225:ADC #0 it, by turning it on or off. ENDPROC 830 .M5: JSR &FFEE:PLA:DEX:BNE With the cursor positioned over the pixel, 420 DEF PROCDISPLAY M4:DEY:BPL M3:LDA #31:JSR press the ENTERS key to set the pixel. You 430 PROCMOVEUDG(1):VDU31,3,3:FOR &FFEE:LDA # 19:JSR &FFEE:LDA delete pixels by plotting them in a different T=224 TO 255:VDU T:NEXT: #13:JSR &FFEE:LDA #227:JMP &FFEE colour, as explained later in this article. PROCMOVEUDG(0) 840 .PSN: PHA:LDA #31:JSR &FFEE:LDA Using these keys, you can design your 440 VDU5:MOVE(16 + X) .32,1023 — #16:JSR &FFEE:TYA:CLC:ADC #16:JSR UDGs quickly and easily. Next week the (16 +Y) .32:VDU224,4:PROCPOINT(0): &FFEE:PLA:RTS second half of the program includes, among PROCGRID:PROCNOS:ENDPROC 850 .ROT:LDY #0:.L2: LDX #7:LDA other things, an option for joystick. 450 DEF PROCMOVEUDG(F) &C18,Y:.L3:LSR A:ROR &70,X:DEX:BPL As you can see, the grid is not the only 460 FOR T=0 TO 31: IF F=0 THEN 480 L3:INY:CPY #8:BNE L2:.L4 LDA square on the screen: there are eight smaller 470 A(T)=T?&COO:T?&COO=B(T): &6F,Y:STA &C17,Y:DEY:BNE L4:RTS ones beneath the main grid, and two smaller GOTO 490 860 .FIN:]:NEXT ones on the right of the grid. 480 B(T)=T?&COO:T?&COO=A(T) 870 IF FIN< >MC+101 THEN PRINT The two on the right of the grid are actual- 490 NEXT:ENDPROC "MACHINE CODE WRONG, CHECK VERY size versions of the UDG you are editing both 500 DEF PROCLOAD CAREFULLY":END normal and reversed. As the pixels are 510 VDU 4: CLS:PROCMOVEUDG(1) 880 ENDPROC changed, these two 'models' are updated, 520 INPUT"ARE YOU SURE (Y/N) ",A$: enabling constant monitoring of your design. IF A$< >"Y" THEN 550 The eight squares below the main 'drawing 530 1NPUT"FILENAME",A$:IF LENA$ > 8 board' are for storing the current bank of THEN 530 When you type in and RUN the program, you UDGs, or what you have already defined. 540 H =OPENIN(AS):FOR T= &COO TO will be presented with two questions, which This means that you can define up to eight &CFF:?T= BGET # H:NEXT:CLOSE # H determine the sort of UDG you define. UDGs and keep them all in memory at any 550 PROCMOVEUDG(0):CLS:PROCDISPLAY: The first of these asks which PMODE you time. Some of these are not always visible. ENDPROC want to use. PMODE4 gives you high reso- This happens when the colours of the plotted 560 DEF PROCSAVE lution UDGs, but in only either green and pixels are the same as the background colour. 570 VDU 4:CLS:PROCMOVEUDG(1) black or buff and black. The second, These are not updated all the time, but only 580 INPUT"ARE YOU SURE (Y/N) ❑ ";A$: PMODE3, gives you half as many pixels across when you store the newly edited UDG, as IF A$< >"Y" THEN 610 (the pixels are twice as wide) but allows you to explained later in this article. 590 INPUT"FILENAME";A$:IF LENA$ > 8 OR have four colours. A$="" THEN 590 The second of the INPUTS lets you deter- CONTROL KEYS 600 H = OPENOUT(A$):FOR T= &C00 TO mine which colour sets you want. Screen 0 in This program has a number of control keys, &CFF:BPUT # H,?T:NEXT:CLOSE# H PMODE4 gives green and black, while in to enable you to use. its numerous options at 610 PROCMOVEUDG(0):CLS:PROCDISPLAY: PMODE3 it gives red, blue, green, and yellow. the press of a key. ENDPROC Screen 1 gives you buff and black in PMODE4, Two of these control keys go hand in hand, 620 DEF PROCPOINT(F) and cyan, magenta, orange and buff in and are fundamental. These are S and G. S 630 PRINTTAB(3+PT,5)"0":PT= (PT+ F) PMODE3. stores the UDG currently in the grid in the AND 31:PRINTTAB(3+PT,5)" A ": After you have made these two choices, you bank. After pressing the S key, the computer ENDPROC cannot then change the PMODE without waits for you to press another key—a number 640 DEF PROCASIGN reRUNning the program but you can change between 1 and 8. This number determines the 650 PROCMOVEUDG(1):FOR T=0 TO 7: the screen. position of the UDG in the bank. This 1520 IFPEEK(343) =223 THENX= X -T 1530 IFPEEK(344) =223 THENX= X +T 1540 IFPEEK(341) = 223 THENY=Y-1 1550 IFPEEK(342) =223 THENY =Y +1 1560 RETURN 2000 GOSUB4000 2010 P =3*Y +INT(X/8):PX =7 -X + 8`INT(X/8) 2020 IF T=2 THEN VL=F-1 ELSEVL= - (F=1) 2030 PK= PEEK(P+VARPTR(A(0))) 2040 PK= PK AND(255.1 -2TPX):IF T=2 THENPK= P1C:AND or use the computer's own characters The Dragon allows larger UDGs (255.1 -2I(PX-1)) 2050 PK= PK FT OR VL.2i(PX +1 -T) enables you to replace any of the bank with 60 DATA 39,5,88,73,122,121,68,167, 2060 POKEP+VARPTR(A(0)),PK updated versions. 128,125,121,68,38,233,140,125, 2070 PUT(216,10)- (239,33),A,PSET G, again followed by a number between 1 76,38,221,57,4496 2080 PUT(216,70) - (239,93),A,PRESET and 8, does the opposite-it takes the UDG 110 CLS:PRINT" SELECT GRAPHICS MODE 2090 RETURN out of the bank and places it in the grid. (3 - 4) "; 2100 RETURN Although the program uses a machine code 120 A$= 1NKEY$:IF A$ <"3"ORA$> "4" 2200 RETURN routine, the process takes a few seconds. THEN120 2300 A$=INKEY$:1F A$ < >"S"AND Picking up a character like this does not 130 T= 5 - VAL(A$):PR1NTA$ A$ < >"L" THEN2300 change the contents of the relevant bank 140 PRINT" SELECT SCREEN TYPE (0-1) "; 2310 IF A$="S" THEN 2330 position-you could pick up the same UDG 150 A$=INKEY$:1F A$<"0"ORA$>"1" 2320 CLOADM:SCREEN1,ST:RETURN as many times as you like, as long as you do THEN 150 2330 CSAVEM"",6800,7679,6800 not store a new design in its place. 160 PRINTA$:ST=VAL(A$) 2340 SCREEN1,ST:RETURN This part of the program has two more 200 PMODE5-T,1 2400 ST=1 -ST:SCREEN1,ST: RETURN control keys. If you press C, you can change 210 DIMA(14),C1(1),C2(1),C3(1),C4(1) 2500 A$=INKEY$:1F A$ <"0"ORA$ > "8" the colour. If you are in the four-colour mode, 220 PCLS4:GET(0,0) - (9,5),C4,G THEN 2500 you can change between any of the four 230 PCLS3:GET(0,0) - (9,5),C3,G 2510 F= ((VAL(A$) -1)AND3)+1:RETURN colours available. If in the two-colour mode 240 PCLS2:GET(0,0) - (9,5),C2,G 2600 A$=INKEY$:IF A$ <"1" ORA$ > "8" you can switch between either of the two 250 PCLS1:GET(0,0) - (9,5),C1,G THEN 2600 colours. You might like to do this to rub out 260 PCLS:SCREEN1,ST 2610 J =VAL(A$) -1 any of the pixels you have set by mistake. 270 C= - 1:F = - 2:GOSUB2070 2620 GET(J .32 + 8,165) - (J*32 + 31,188),A After pressing the C key, tell the computer the 280 FORX=8T0255 STEP32:C= (C +1) 2630 GOSUB3000:G0T02070 number of the new colour you want. AND3:COLORC + 1:LINE(X,165) 2700 A$=1NKEY$:IFA$<"1" ORA$ > "8" The last control key in this half of the - (X + 23,188),PSET,BF:NEXT: THEN 2700 program is T. This allows you to either LOAD COLOR6-T 2710 J = VAL(A$) -1 in a previously SAVEd bank of UDGs, or to 290 FOR X =3T0147 STEPT*6:LINE 2720 PUT(J .32 + 8,165) - (J`32+31,188), SAVE the present one. (X,3) - (X,147),PSET:NEXT A,PSET 300 FORY=3T0147 STEP6:LINE(3,Y) 2730 RETURN Ii - (147,Y),PSET:NEXT 2800 RETURN If you have a Tandy, you should make these 310 X =12:Y =12 2900 RETURN changes to the following program: change the 320 X1 = X*6 + 4:Y1 = Y*6 +4 3000 CL= F:P0KE30999,T -1:N =USRO number 139 in the DATA statement in Line 50 330 PUT(X1,Y1) - (X1 + 5*T- 1,Y1 + 4), (VARPTR(A(0))) to 179 (the 139 is in bold type); change the C1,NOT 3010 FORK = OT023:FORJ =01023 number 48 in the DATA statements in Line 50 340 A$=1NKEY$ STEPT: F = PEEK(31500 + r24/T + to 237 (the 48 is in bold type); change the 350 GOSUB 1500 J/T) + 3 - T number 223 in Lines 1520 to 1550 into 247 360 IF A$="" THEN 380 3020 X1 =J`6 +4:Y1 = K*6 +4 and the 4496 in Line 60 to 4725. 370 ON INSTR("PCTRGSMIV",A$) GOSUB 3030 GOSUB4000:NEXTJ,K:F=CL: 2200,2500,2300,2800,2600,2700, RETURN 2900,2100,2400 4000 ON F GOTO 4010,4020,4030,4040 10 CLEAR200,30998:DEFUSR0 = 31000 380 IF Y<0 THEN Y=23 4010 PUT(X1,Y1) - (X1 + 57-1, 20 T= 0:FORK = OT043:READN: 390 IF Y>23 THEN Y=0 Y1 + 4),C1,PSET:RETURN T=T+N:POKEK+31000,N: 400 IF X<0 THEN X=24-T 4020 PUT(X1,Y1) - (X1 + 5 .T -1, NEXT:READC:IF T< >C THEN PRINT 410 IF X>23 THEN X=0 Y1 + 4),C2,PSET:RETURN "DATA ERROR":END 420 GOTO 320 4030 PUT(X1,Y1) - (X1+5 -1-1, 50 DATA 189, 139, 48,31,3,142,123,12, 1500 PUT(X1,Y1)- (X1 + 57-1,Y1 +4), Y1 +4),C3,PSET:RETURN 230,192,134,8,183,121,68,79,88, C1,NOT 4040 PUT(X1,Y1)- (X1+57-1, 73,122,121,68,125,121,23 1510 IFPEEK(338) =191 GOSUB2000 Y1 + 4),C4,PSET:RETURN Spectrum sound effects are limited with the BASIC BEEP command. But with the machine code out you can make sirens and laser zaps—as well as a seven-colour screen border
Normally the microprocessor addresses the computer's memory. And with many home micros if you want to access an outside device—like a printer, a TV or even the computer's own keyboard—you have to do it via a memory location which is tied to an output port. With Z80 micros such as the Spectrum, though, you can access the ports directly. It allows you to do this both in BASIC and in machine code via the BASIC commands IN and OUT and assembly language mnemonics in and out. WHAT IS A PORT? A port is the channel of communication between the computer and the outside world, and here the outside world includes the keyboard which is a peripheral as far as the microprocessor and its associated ROM and RAM are concerned. You have already seen how the BASIC IN command can be used to access a joystick (see page 465) and how the assembly language in can be used to access the keyboard (see page 482). The OUT and out commands work in much the same way, only they send data out to the peripherals, rather than taking data in from them. They can be used to control the border of the TV screen, and both commands can be used to output sound through the Spectrum's speaker in a much more adaptable fashion than the BASIC BEEP command. But here, the machine code out is under examination, as the BASIC OUT is rather slow. You need the speed of machine code because of the way that out is used to generate sound. What you are doing is to move the speaker in and out. If you do this once, it produces a click, like you sometimes get when you first switch on a record player. But the trick is to do this repeatedly, and very quickly. If the speaker clicks fast enough, a succession of clicks will blur into a low-pitched buzz—if it does it faster still the pitch of the sound will go up. SOUND OUT The following assembly language routine makes a sound whose pitch increases. Type CLEAR 64599 then enter: WHAT A PORT IS OUTING TO THE BORDER SHIFTING AND ROTATING SPECIFYING THE COLOUR MAKING THE SPEAKER MOVE GETTING THE TIMING RIGHT PAUSE LOOPS COARSE AND FINE TUNING SETTING THE PITCH DOUBLING THE PITCH
org 64600 It is port 254 that controls the Spectrum's So to make sure that the border colour Id a,(23624) speaker. But the same port also controls the doesn't change during the sound effect, bits rrca TV border colour. When you out a sound you three, four and five have to be shifted three rrca don't want to change the border colour as places to the right (into zero, one and two). rrca well, so you have to do a little routine to leave Id b,0 it unaffected. SHIFTS AND ROTATES loop push bc First, you load the accumulator with the There are several commands that can do this, xor 16 contents of the system variable in memory but the one selected here is rrca—rotate right, out 254,a location 23,624. The Spectrum's colours are with carry, on the accumulator. This instruc- pause nop specified by a number between 0 and 7. tion moves all the bits in the accumulator one nop Normally, the bits that control the border place to the right. It is called a 'rotate' because djnz pause colour are bits three, four and five. But when the contents of bit zero are moved round and pop bc you are controlling it through port 254, it's put into bit seven. A simple shift moves each djnz loop bits zero, one and two that temporarily bit one place to the left or right, but fills the ret change the border colour. spare bit with a zero. Shifts are used in arithmetic operations. You can see that a straight shift to the left multiplies a number by two, and a shift to the right divides by two. Here, though, a rotate is used because you only care about shifting three of the bits. The contents of the other bits don't matter. The rrca also copies the contents of the zero bit into the carry flag. But again, it doesn't matter what the value of the carry flag is, because it is not examined. To shift the border colour's bits three places to the right, rrca is performed three times. This effectively divides the border colour by eight. But then, when the border colour was stored in bits three, four and five the colour (normally a number between 0 and 7) is already multiplied by eight. So now, when the out command is used, it will specify the same border colour as before and no change will be detected. SETTING THE COUNTERS The B register is going to be used as a double counter. To start with, it is loaded with 0, and that value is copied onto the stack by push bc. The B register cannot be pushed onto the stack by itself. The stack commands, push and pop, only work on register pairs, so B has to be pushed onto the stack together with the contents of the C register. But as you are not going to do anything with C it won't effect the program. OUTING THE SOUND Bit four of port 254 command controls the Spectrum's speaker. By flipping this bit, the the pause loop executing them many times. The djnz works on the B register. So the first time round the loop it decrements B from 0 to 255. Then it goes round the pause loop a further 255 times until it has decremented to How many ports are there? 0. Theoretically there are 64K possible Once it has come out of the pause loop the ports—that is the maximum number that last item is popped off the stack, back into the can be addressed by a 16-bit register. BC register pair. This restores the value of the But in practice only a few of the possible B register, then djnz decrements it again and ports are used. Only one port is used sends the processor back round the loop loop when your Spectrum is in an ordinary again. This pushes the BC registers back onto hardware configuration—port 254. the stack. So each time the processor goes With the in command you have seen round this loop the counter on the stack is how different parameters feed into the decremented and the starting value for the instruction direct the port to different pause loop in the B register is one less each areas of the keyboard (page 482). And in time. So the pause is executed one less time this article, different bits of the machine and the pitch increases. code out command can be used to control the different standard peripheral SEVEN - COLOUR BORDER devices. When you specify the BORDER colour in However, if your Spectrum is coupled BASIC, you assign it a number between 0 and to other non-standard devices other 7. Then the whole border turns that colour. ports can be used. A simple example is But the following routine uses the machine when a Kempston joystick is plugged code out command to give a seven-colour into your Spectrum; port 31 is used to border. It could give you an eight-colour access it (see page 465). border but there is no point in having one of And if you are a dab hand at the border colours the same as the screen electronics you could link up your colour. Spectrum to control your central heating system or your org 64600 electronic synthesizer redo halt through different ports. xor a loop out 254,a speaker's diaphragm is sent in and out— Id b,205 creating sound. Bit 4 is flipped by pause Id e,2 exclusively-oring it with 16. So if bit four is inner dec e set—that is, it's 1—it is reset to 0. If it is reset jr nz,inner to 0, it gets set to 1. djnz pause The out 254,a then outs the contents of the Id d,a accumulator through port 254. (Note that on Id a,$7F most commercial assemblers in and out in- in a,254 structions need brackets round the port num- rra ber. So if you are not using the assembler rts nc published in INPUT, this instruction should Id a,d read out (254),a.) inc a cp 7 SETTING THE PITCH jr nz,loop The instruction nop means no operation. It jr redo does nothing at all and translates into 00 in machine code hex. The instruction does take SYNCHRONIZING THE SCREEN some time to execute though—approximately The halt instruction waits for an interrupt to 1 microsecond, that's a millionth of a second. occur, then sends the processor onto the next The reason it is used here, twice, is to slow the instruction. With the Spectrum the interrupt processor down as it executes this loop. The occurs in time with the screen scan. So halt speed that the processor goes round the loop starts this routine off when the scan starts at controls how fast the speaker's diaphragm the top of the screen, synchronizing the goes in and out and, consequently, the pitch. border bands with the edge of the TV screen. But as you can see the nops are not just The xor a exclusively-ors the accumulator executed twice. The djnz—decrement and with itself, which is a quick way to set it to 0, jump if not zero—sends it round and round and the 0 is outed through port 254. Zero, in makes a relative jump back to the label inner if the result is not zero. So this inner loop is performed twice each time the processor goes round the outer loop. The outer loop is performed 205 times with the B register. It is made up of the Id b,205 which loads the number into the B register and the djnz which decrements the B register and jumps if the result is not zero all in one. There is no similar instruction that works with the E register. That's why the decrementing and jump have to be done using two separate instructions. If you try altering these two values you will see how the value put into the E register alters the width of the bands a lot, while the value put in the B register only alters it a little. CHECKING FOR BREAK At some point you will want to escape from this routine. And to do that without switching your computer off you must include an escape routine. The one used here checks to see if the IBREAKI key has been pressed. This is done using the in instruction. But first, Id d,a loads the contents of the accumulator in the D register. The ac- cumulator is going to be used for something else for a moment and the D register is doing nothing, so it can be used as a temporary store. The accumulator is then loaded with the hex number 7F. This number specifies the bottom righthand corner of the keyboard (see page 465). Then in a,254 takes the bit pattern representing the status of the bottom right- hand section of the keyboard into the accumulator. It is bit zero that denotes the state of the IBREAKI key. If the IBREAKI key is not being pressed, bit zero is 1, but if it is being pressed bit zero is 0. A quick way to check this is to rotate bit zero—which is at the extreme righthand end of the register—into the carry flag, then check machine code as well as in BASIC, means on the status of the carry flag. The rra does the black. So the top part of the screen starts off rotation, and the rts nc returns to BASIC black. when there is no carry. So when 'BREAK' is pressed and bit zero is changed from 1 to 0, ADJUSTING THE PAUSE the rts instruction breaks out of the routine. In this routine the timing is critical. The Otherwise it continues. (Note that the con- length of the pause will specify the width of ditional return takes the form rts only with the bands of colour on the border. So the the assembler published in INPUT. Other pause here is controlled by two loops—the Spectrum assemblers use the standard ret inner loop which sets the delay coarsely and with conditional returns.) the outer pause loop which fine tunes the delay. CLOSING THE LOOPS The inner loop is performed on the E Once you have a way out of the routine, the register, which is set to 2 by Id e,2, and value of the accumulator is restored by Id decremented by dec e. The jrnz,inner then a,d—it just loads the number temporarily stored in D back into A. been copied into the B register it is pushed Then A is incremented to specify the next back onto the stack. Now it is both in the B colour. This is compared to the number 7 by register and on the stack. cmp 7. Seven is the number that specifies The next pause loop works on this initial white, and white is the colour of the screen. value of B. Then the initial value of the B So if the number in the accumulator is not register is popped back off the stack again. that specifying white, the jrnz,Ioop jumps This has to be done every time after a djnz back to out the colour for the next band. And Making Music on the Spectrum instruction to restore the value of the B when this loop has counted up from 0 to 7, the Using the machine code out it is possible register. When the processor comes out of a processor moves onto the jr redo which takes to make music on your Spectrum. But djnz loop its value must be zero. it right back to the beginning again to wait for adjusting the pause loop to get the pitch The initial value of the B register is then the next screen scan. you require is laborious. decremented. If it is not zero, the processor You'll notice that you don't have to worry It would be much easier to write a loops back to the beginning of the loop loop about making sounds by accident when routine which you could feed two and the whole routine is performed again with changing the border colour. The routine does parameters—related to pitch and a lower value of B. And on the 256th pass, not affect bit four which moves the speaker. duration—into. Fortunately, this has al- when B is finally decremented to 0, the The highest number outed here is 7 and the ready been done for you in the ROM. It is processor moves onto ret and returns to lowest number that would affect bit four is 16. called the BEEP routine and it starts at BASIC. 03F8. And there is an additional subrout- loop is perfor- SOUND EFFECTS You will see that the pausea ine at 03B5 called BEEPER which uses the med 256 times on the first pass, once on the The time has come to tackle a more complex value in H L to control pitch and the value second pass and then one more time each time sound effect using the out command. The in DE to control the duration. the main loop is executed. But the pauseb loop following routine makes a Star Wars-style The pitch value you need to put in H L is is performed 256 times on the first pass and laser zapping sound using the combination of given by 437,500/f-30.125, where f is the one less time for each time the main loop is a tone of rising pitch and one of falling pitch. note's frequency. Multiply frequency by executed. duration required to give the number you org 64600 ADDING NATURAL TONES Id a,(23624) put in DE. There is no 10-second limit on rrca the duration of the note when you are using The sounds that computers produce usually rrca this method. sound very synthetic because they are too rrca If you call the BEEP routine directly pure. Musical instruments and other devices that generate sound in the outside world tend Id b,0 the same values for duration and pitch to be rather haphazard in the way they loop push bc used with the BASIC BEEP should be produce noise. But it is this very randomness xor $10 pushed onto the stack. that makes the sound pleasing to the human out 254,a ear. An instrument plays not only the funda- push af by $10 which is 16 in hex. This makes the xor a mental pure tone but also harmonies of it. sound. sub b There is a way to add a random factor to But then the contents of the accumulator your sound effects on the Spectrum, though. Id b,a are pushed onto the stack—along with the pop af The RAM between 16,384 and 32,767 is on contents of the flag register. Registers have to pausea nop chips that are frequently interrupted by the be pushed in pairs. The xor a clears the djnz pausea Uncomitted Logic Array which looks after accumulator and sub b takes the contents of xor $10 the TV picture and performs other hardware the B register away from 0—the contents of out 254,a duties. A—and stores the result in A. This effectively pop bc Normally, these interruptions are so inverses the contents of B. When B is 255, the push bc quick—typically a couple of microseconds— result of the subtraction is 1. And when B is 1, pauseb nop they are not noticed. But sounds are so time the result is 255. djnz pauseb dependent that the ear can sense the slightest The Id b,a loads the result of the subtrac- variation. So if you put your sound effect pop bc tion back into B. Then the contents of the djnz loop programs in this area they will be given a accumulator which were stored on the stack ret more natural, random feel—and they will last are popped off again, back into the slightly longer. The first four instructions of this program are accumulator. Unfortunately, the assembler given in exactly the same as the first four in the other The contents of the accumulator are INPUT occupies this area of memory. But if sound out program. Remember that these popped back off the stack. Then there's a no printer is being used you can assemble preserve the border colour. pause loop that counts down the contents of your sound effects programs in the printer The next two—which initialize the two the B register—djnz decrements the B register buffer, if they are short enough. The printer counters, one in the B register and one pushed and tests for zero, remember. And bit four is buffer lies between 23,296 and 23,552. So you from the B register onto the stack—are the flipped and outed to the speaker. can use 23,296 as your origin. And as the same as well. And so are the next two which The initial value of the B register is then printer buffer is protected against overwriting xor bit four with 16 and out the result through restored by popping it off the stack. But this by the BASIC you will not have to do a CLEAR port 254, though this time the xor is suffixed value will be needed again later, so once it has before assembling.
CUMULATIVE INDEX
An interim index will be published each week. There will be a complete index in the last issue of INPUT. Dragon 596-597 disk, Commodore 64 Protecting disks and tapes 683 676-682 A Electronic mail 614 modifying programs for Protecting programs 459-463 Adventure games, Ellipse, drawing a Spectrum microdrive 616-621 using the text compressor 684-689 Commodore 64, Dragon, program squeezer Applications Tandy, Vic 20 581 Acorn 546-552,593-595 Q CAD 566-572,573-577 Epson codes 646-647 Dragon, Tandy 637-641 Quote mode 520-527 conversions program Escape codes 646 sound effects, Spectrum 728-732 Commodore 64 420 extend your typing 498-503 Memory 721-727 UDG designer saving, Acorn 546-552 ASCII codes 420-421 F SAVEing on tape R Files, using 622-627 532-533 ROM graphics ASCII files 622-623 Microdrives 505 commands for Commodore 64 420 Assembler saving and loading on 616-621 Dragon, Tandy 440-444 Acorn 626-627 Modems 612-615,712-714 ATTR, Spectrum 656-658 Dragon, Tandy 627 Monitors and TVs 445-449 S Autorun 460-461 Commodore 64, Spectrum,Vic 626 Motion Screen pictures Axes for graphs 415-416,470-471 FLASH command from UDGs 484-491 Spectrum 434 equations of 584-592 Multicoloured background 490 Seikosha codes 647 Flight simulator 716-720 B Music Serial access Barchart 470-476 musical keyboard 672-674 tape systems 505-506 Basic programming G scales 670-672 Sort routines 708-711 Games programming 708-710 bouncing ball graphics 584-592 transcribing 702-703 delayed replacement Commodore 64 adventures, planning your own 422-427 insertion 710-711 graphics 420-421 duck shooting game 492-497 quick 711 716-720 N defining functions 578-583 flight simulator scatter 710 pontoon game 535-540,553-559 Networks 614,715 detecting collisions 656-661 Space station, formatting 433-439 text compressor drawing a 666-668 628-636,648-655,684-689 Speed POKE making more of UDGs O Graphics, CAD program 566-572 Dragon, Tandy 444 450-457,484-491,528-533 On-board graphics more music 701-707 Graphics, ROM Commodore 64 420 Spelling-checker 543-544 420 plotting graphs 413-419,470-476 Commodore 64 OUT, Spectrum 728-732 Storage devices 504-508 Graphs 413-419 probability 694-700 String functions 512-513 protecting programs 458-463 Grid, drawing a Acorn, Spectrum 581 P Stunt rider UDG, Vk 20 429 simple music 669-675 Parameters for functions 578-583 sort routines 708-711 Submarine UDG, Vic 20 430 H Pascal's Triangle 697 SYS using files 622-627 Histograms and barcharts 470-476 Pie charts 474-476 Commodore 64, Vic 20 463 wireframe drawing 509-513,560-565 PEEK, Commodore 64 605-611,662-668 Vic 20, 656,658-659 Bootstrap programs 459-463 Imperial to metric Peripherals T Bug tracing 477-483 Tape storage 504-505 conversions 520-527 bulletin boards 712-715 Bulletin boards 613,712-715 data storage devices 504-508 Teletext 614,715 Bytes, saving Interest on savings Text compressor program 583 light pens 690-693 Acorn 546-552,593-595 modems 612-615 628-636,648-655,684-689 Inversing the screen Tokens ZX8I 432 setting up a printer 642-647 TVs and monitors 445-449 Commodore 64 42' C Trace program Cardgame graphics 534-540 wordprocessors? 541-545 J Spectrum 477-483 Cassette storage 504-505 Planning screen displays 433-439 Joysticks, Commodore, Vic 20 514-519 Character sets duck shooting game 492-497 POINT, Acorn 656,659-660 TVs and monitors 445-449 redefining 450-457 in games 464-469 Dragon, Tandy 556,660-661 Pontoon program 534-540,553-559, Typing tutor part 4 498-503 Collisions, detecting 656-661 JOYSTK - 598-604 Communications 612 615 Dragon, Tandy 468-469 Computer Aided Design, Jungle picture 485-491 PPOINT, Dragon, Tandy 656,660-661 U program 566-572,573-577 PRINT 434-438 UDGs Control commands, Acorn, Commodore 64, 484-491,528-533 animals in wordprocessing 545 K Spectrum, Vic 20 434 450 creating extra Conversion program 520-527 Keyboard, as a musical instrument PRINT AT 721-727 program to design 672-674 Acorn 434 452-457 redefining numbers Spectrum 434,436 User defined functions 578-583 D PRINT SPC Data storage 413 L Commodore 64, Vic 20 434-435 623-624 Legends Datafiles PRINT TAB Defining functions 578-583 for graphs 416 V Acorn 434,438 Dip switches 646 Letter frequency, Videotex 614,715 Commodore 64, Vic 20 435 for text compressor 636 Viewdata 715 Disk drives 506-508 Spectrum 434 Light pens 690-693 Virtual memory 545 converting programs for, PRINT @ Commodore 64 676-682 Volatile storage 504 Dragon, Tandy 435 Displays, improving 433-439 PRINT #, Commodore 64, Vic 20 644 697-700 M Distribution curves Machine code programming Printers, setting up 642-647 Drawing in 3D 560-561 animation control commands 644-647 Wireframe drawing, Duck shooting game 492-497 - 512 Vic 20, ZX8I 428 432 Program squeezer and colour 662-668 assembler Acorn 546-552,593-595 combining images 560-565 E Dragon, Tandy 430-444 Dragon, Tandy 637-641 in 3 dimensions 477- 605-611 Editing programs Spectrum 482 Program symbols with perspective Commodore 64 420 modifying programs for Commodore 64 420 Wordprocessing 541-545
The publishers accept no responsibility for unsolicited material sent for publication in INPUT. All tapes and written material should be accompanied by a stamped, self-addressed envelope. JFind out the BASIC needed to plot the TRAJECTORIES of flying objects—a principle with many applications
JComplete your UDG GENERATOR with new routines to enable quick, easy manipulation of the finished designs
Discover DATABASE MANAGEMENT SYSTEMS, and how to make really good use of your files
_/ Continue the FLIGHT SIMULATOR program by finding out how to set the aeroplane in motion
JPlus, a machine code routine for the COMMODORE 64 to give you BASIC control of HI-RES GRAPHICS