System Review The HP-41C: A Literate Calculator?
Brian P Hayes Scientific American 415 Madison Ave New York NY 10017
Calculator vs Computer can be full of surprises, often to the frustration of the pro The computer and the programmable calculator seem grammer. to be following paths of convergent evolution. As the one The HP-41C, which was introduced by the Hewlett- is made smaller while the other gains in capability, the Packard Company about a year ago, is among the pro line of demarcation between them becomes more and grammable calculators that lie closest to the computer more arbitrary. For now at least, the programmable borderline. It comes close enough for the jargon of com calculator remains a distinct and lesser species, but it puters to be useful in describing it. At the Corvallis Divi shares many of the attributes of the computer. Moreover, sion of Hewlett-Packard, where the HP-41C is made, the shared attributes are chiefly the ones that make the they refer to the calculator itself as the ''mainframe" and computer an interesting machine. Both devices offer an to its accessory devices as the "peripherals." The intimate acquaintance with the powers and pleasures of calculator comes equipped with four input/output (I/O) algorithms. Both exhibit an enigmatic unpredictability: ports, through which the various elements of the system the response of the machine to any given stimulus is are interconnected. Because the peripherals do some data wholly deterministic, yet the behavior of a large program processing internally, the system might even be said to have "distributed intelligence." When compared with a computer, most programmable calculators have a rich instruction set, but they are defi cient in memory capacity and in facilities for communica tion with the user. A calculator comes with such amenities as trigonometric, logarithmic, and statistical functions built in; with a computer, even floating-point arithmetic must usually be constructed out of software. On the other hand, no calculator has the memory needed to store large tables or other data structures. And it is the communication problem that most seriously limits the utility of the calculator. A display that can represent only the 10 digits, a decimal point, and a minus sign does not have much range of expression. Even for problems that have entirely numerical results, such a display is not always adequate, since without labeling of any kind it is easy to become confused about what a number means. The HP-41C In the HP-41C, the instruction set is at least the equal of that in any other calculator and the potential memory space is large (although it can never be large enough). The most conspicuous distinguishing features, however, have to do with communications and "human factors " Photo 1: Components of the Hewlett-Packard HP-41C (or, in other words, those things that aid in writing pro calculator system. Shown here are the calculator itself and three grams and in interpreting their results). peripheral devices: a magnetic-card reader, a wand for reading All three of the peripheral units now available serve to printed bar codes, and a thermal dot-matrix printer. The peripheral units plug into four ports at the top of the calculator, get information into or out of the HP-41C; they are a which can also receive modules containing additional memory printer, a magnetic-card reader, and a wand for reading or precoded applications programs. The HP-41C alone costs bar codes. But perhaps the most significant innovation of about $300; a system including all three peripheral devices and all is in the calculator itself: a liquid-crystal display that two memory or applications modules is about $1000. (Photo by can represent not only numerals but also the complete Ed Crabtree.) uppercase alphabet and a few lowercase letters and other
118 January 1981 © BYTE Publications Inc symbols. The letterforms are crude but perfectly legible; operation of the calculator can be illustrated by consider what they bring to the calculator is literacy, and it makes ing one of the curious challenges of calculator design. all the difference in man-machine relations. The architecture of the HP-41C is not fundamentally Mnemonic Functions different from that of its predecessors in the Hewlett-' The problem is that most scientific calculators have Packard line. There is a four-level stack of registers where more instructions than they have keys; in the case of the pending operands are generally held; other registers are HP-41C, there are more than 130 instructions and only identified by a 2- or 3-digit address. The internal memory thirty-five keys. A shift function doubles the number of consists of 63 registers, but this number can be increased distinguishable key sequences, but that still leaves almost by plugging memory modules into the ports. Each half the instruction set without a home on the keyboard. module adds 64 registers, so that a full complement of Rather than further increase the number of keys or the four modules yields a total capacity of 319 registers; with number of shifted modes, Hewlett-Packard has adopted a all the ports occupied, however, no peripheral devices solution familiar in larger systems: all instructions, can be connected. whether or not they appear on the keyboard, can be ex The memory available can be divided in any way ecuted by spelling out their mnemonic in the display. desired between data storage and program storage. When Programs resident in memory and instructions associated allocated to data memory, a register holds a single with peripheral devices can be executed in the same way. floating-point number (10-digit mantissa and 2-digit ex Execution of a mnemonic label has the significant ad ponent). Program capacity is more difficult to measure vantage of eliminating all dependence of the instruction because instructions have varying space requirements. set on the layout of the keyboard. It also has certain Without extra memory and with a reasonable allowance potential drawbacks that the designers of the HP-41C for data storage, the maximum for an unassisted HP-41C have gone to some lengths to remedy, largely by ex usually falls between 150 and 200 program lines. By add ploiting the alphabetic display. For example, if the spell ing three modules and keeping the same data space, the ing of a mnemonic is forgotten, a complete listing of the program capacity is expanded to about 1200 lines. instruction set can be called up by the CATALOG func An additional wider register is dedicated to alphabetic tion. operations. Up to 24 characters can be accumulated in the Another objection is that repeatedly spelling out a alpha register, although only 12 at a time fit in the liquid- function can be tiresome on a keyboard smaller than the crystal display; the extra characters scroll in to the left, human hand. This burden has been relieved by the marquee-style. The alphabetic capability is not a mere radical strategy of allowing all the keys to be redefined by frill. The extent to which it is called upon in the everyday the user. Any instruction (with the exception of a few program-editing pseudoinstructions) and any program can be assigned to any key. The fluid indeterminacy of the keyboard leads to a fur ther possible complaint: the user may lose track of what REMOTE I/O function has been assigned to a particular key. Two devices come to the aid of the forgetful. A keyboard overlay slides into place to relabel the keys according to the chosen assignments; if several programs require dif ferent key assignments, a separate overlay can be made up for each one. The second aid is more elegant: the cur rent function of any key can be verified merely by press ing the key and holding it down a moment. The mnemonic of the function appears in the display. If the key is released, the function is executed; otherwise, the word "null" appears and the command is canceled. [A third aid to the use of the HP-41C keyboard is the selection of the user/standard mode. The key redefini tions are valid only when the calculator is in the user mode. To use a key that has been redefined for its Control AND monitor remote devices original function, the user has only to press the USER key Real time clock/calendar included to toggle the calculator back to its standard mode. In the • An AC carrier communications I/O interface for the APPLE II* standard mode, the HP-41C behaves as it would before computer. Output communications operate up to 256 BSR System X-10* control modules. Input communications come from the X-10 any keys were assigned, thus giving the user the best of command console, and temperature and security input modules, both worlds. . . . GW] soon to be available from Intelligent Control Systems, Inc. • Software routines are provided to handle the AC I/O, to set, read, and display the real time clock, and a background schedule Further Features for the Programmer control program. 4 selectable interrupt rates allow machine The versatility of the liquid-crystal display is exploited language programs to run simultaneously with other programs. • Real time clock provides sec, min, hour, date, day of week, mo, in several other ways to make the HP-41C friendly and and year. Rechargable battery runs clock when APPLE is off. fool-resistant. A row of indicators below the main • Trademarks-APPLE II: Apple Computer Inc.,System X-10: BSR Ltd. SEE YOUR APPLE DEALER FOR A DEMONSTRATION.. .$185 sugg. retail display provides various indications of mode and status. Error messages can be reasonably explicit: an attempt to Intelligent Control Systems, Inc. divide by 0 elicits "data error," and a number greater POBOX14571»MPLS,MN 55414* (612) 699-4342 than 10" is flagged as "out of range." When a conditional
120 January 1981 © BYTE Publications Inc Circle 71 on inquiry card. Circle 72 on inquiry card. test, such as "X = 07", is executed from the keyboard, long program requires several cards, and a routine that the display answers the question "yes" or "no." saves the state of the entire machine sometimes calls for a Alphabetic text can also have a valuable role within a whole deck of them. program. How it is employed is largely up to the pro Cues provided by the calculator make operations with grammer, but two obvious uses are prompting for inputs the cards almost mindless. When writing a program onto and labeling outputs. cards, a message in the display indicates how many Even with the best of keyboard technologies, entering a tracks will be needed; when reading a program, the same long program is inevitably tedious. A feature of the HP- message gives the lowest-numbered track that has yet to 41C that helps in avoiding needless repetition of effort is be read. The cards can be inserted in any sequence, and a continuous memory, which maintains all data and pro the information is sorted out internally. A defective card grams even when the calculator is turned off. Key or an unsuccessful pass through the slot generates an ap assignments, the settings of flags, and other status infor propriate error message. mation (such as the angular mode) are also preserved. A Cards can be both written and read at the command of program that is run frequently can be kept in the a running program. For example, a data card might be re calculator. Memory resources are finite, however, and on quested during an initialization routine, and new values occasion a program must be cleared to make room for might be written onto the card at the end of a calculation. another and later reloaded. It is for such purposes that Or one of several possible subroutines might be appended the magnetic-card reader and the bar-code reader are in to a running program once the program had determined tended. which subroutine was needed. Unfortunately, all these procedures still require human intervention for the actual Using Cards insertion of the card. Thus, the user must attend the The magnetic-card reader, which occupies one port, is machine and feed it by spoonfuls on demand. a small unit that clips onto the top of the calculator and An amusing feature of the card reader is its ability to can be left in place. The cards are the standard 1 by create "private" program cards. When such a card is read 7 cm magnetic strips (slightly smaller than a stick of back into the calculator, the program appears in the chewing gum) that are also employed by the HP-67 and catalog and becomes available for execution, but it can HP-97 and by some Texas Instruments calculators. They not be examined, modified, or copied onto another card. are inserted in a slot at the side of the reader and pulled Any attempt to do so is blocked by the imperious through by a motor for retrieval on the other side. Each message "private." The security measures seem to be ef card has two tracks and each track holds the contents of fective (although I have not worked seriously at 16 registers, which can be either data or programs. A penetrating them); how often they will be needed is another question. In the realm of very-small-scale systems, the major worry is theft of hardware, not soft ware.
Software Compatibility The introduction of a new model computer often raises questions of software compatibility. In this case, Hewlett-Packard has made the new machine compatible with the old software by including a translator routine in the card reader. Magnetic cards written on the HP-67 or HP-97 can be entered into the HP-41C and, with no in tervention by the user, will be converted into HP-41C programs. Thus, the machine has access to the large body of software written for the earlier calculators, including more than 3000 programs in a users' library administered by Hewlett-Packard. An incidental benefit is the addition of more than a dozen instructions peculiar to the HP-67 and HP-97 that become available on the HP-41C whenever the card reader is plugged in, even though most of those instruc tions have nothing directly to do with card operations. For example, there is a block-memory swap that comes in handy occasionally. Bar-Code Wand One drawback of magnetic-card recording is the cost of the medium: roughly fifty cents a card, plus the con siderable expense of the card reader itself. There is also the delicacy of the iron-oxide surface, which necessitates careful storage and the maintenance of duplicate copies for backup. A second input device for the HP-41C, the bar-code reader, relies on the most inexpensive of all known storage media, ink on paper. The reader is a
122 January 1981 © BYTE Publications Inc Circle 73 on inquiry card. Circle 74 on Inquiry card. —^^- hand-held wand similar to a general-purpose one in The situation is somewhat different, however, for troduced some months ago (the Hewlett-Packard those whose main interest is in writing their own pro HEDS-3000), but it has an interface and a plug specifical grams rather than in running other people's. The trouble ly adapted to the HP-41C. is that bar code, for now, remains largely a one-way With programs encoded and printed by Hewlett- channel of communication. Packard, the wand works extremely well. A line of code It is possible to assemble by hand a bar-code represen can be scanned in either direction, although multiple lines tation of a program. The basic materials are adhesive must be read in sequence. The calculator display prompts labels, each bearing the code for a single instruction or a for the lowest-numbered line not yet read. Even more single numeric or alphabetic character. [The "paper helpful is audible confirmation. After each successful keyboard" can also be photocopied, with a program be pass, the calculator emits a high-pitched beep; a failure ing created by cutting and pasting photocopied bar-code results in a lower-pitched tone. The speed and orientation keystrokes. . . . GW] A long program, however, would of the wand are not critical, and with practice the success require several hundred labels; moreover, they must be rate becomes quite high. scanned as a series of many short strokes. The ability to The wand can also do a few things besides the reproduce the program by photocopying might straightforward loading of programs. Individual instruc sometimes compensate for this inconvenience, although tions can be executed from a "paper keyboard" (which is the wand owner's manual warns that such copies may not a table of bar codes, each of which is a single HP-41C in always give acceptable results. (Three copying machines I struction); data can be entered directly into designated tried all produced readable images, although the error storage registers; subroutines can be appended and pro rate was somewhat higher than with originals.) grams merged. One wand function, instead of translating For those who have access to a computer system that the scanned bar code into HP-41C operation codes, includes a daisy-wheel printer or a plotter, Hewlett- displays the actual binary value represented by the bars. Packard will supply programs in BASIC or FORTRAN Printed machine-readable code is an ideal medium for that will generate bar code in the HP-41C format. A far the mass distribution of programs, and Hewlett-Packard more appealing method would be to produce the bar code will reportedly make all its software for the HP-41C on the printer in the HP-41C system; if that could be available in this form. Programs from the users' library done, the wand might entirely displace the magnetic-card will also be offered in bar code, presumably at a lower reader. The HP-41C printer can readily be made to price than programs on magnetic cards. For frequent generate patterns that superficially resemble bar codes. In users of such prepared software, bar code seems to be the several weeks of experimenting, however, I have been medium of choice. unable to persuade the wand to recognize those patterns ?? Micros aren't just for games anymore.. AARDVARK gets down to brass TAX. W
AARDVARK SOFTWARE takes home com face). You simply copy the totals onto your IRS puter use one practical step further with "Per forms. sonal Tax," a federal income tax program This spring, use your microcomputer to designed specifically for home use. simplify your taxes and file with confidence! "Personal Tax" was developed by CPA's You won't have to spend half of your refund and computer professionals. It will calculate either. The "Personal Tax" program is very Federal Forms 1040 and 4726, as well as sched affordable at only $75. ules A, B,G and TC. The program features mul "Personal Tax" will run on: Apple II,TRS-80 tiple entries for a variety of inputs (e.g. wages, Models I and II, and OSI. Additionally, under dividends and charitable contributions). An in CP/M, the program will run on Vector Graphics, dexed instruction manual and easy-to-follow North Star and Cromemco. input forms are included. Minimum machine requirements: "Personal Tax" computes quickly and 48K and one disk drive. accurately, then displays or prints the totals Send check or money order, or, write us for automatically (using a standard printer inter more information. A A R D V A R K S O F T W A R E I N C The Microcomputer People for Professionals 783 NORTH WATER STREET MILWAUKEE WISCONSIN 53202 4 i 4/289-998B
124 January 1981 © BYTE Publication* Inc Circle 75 on inquiry card. SORCERER* reliably. The printer output itself, which is made up of blue or purple characters, is not recognized at all by the wand, and photocopies give erratic results. SOFTWARE! Even if the problems of color, contrast, and resolution Unless otherwise noted, all programs are on cassette and could be solved, there would remain other impediments. require only 8K of memory. The bar pattern for most of the instruction codes exceeds FORTH the capacity of the print buffer; what is more, with no new! Now Sorcerer owners can enjoy the convenience and speed of the fascinating FORTH means of summoning up operation codes from program programming language. Based on FIGFORTH and written by James Albanese, this version was designed especially for the Sorcerer and includes the capability to read and write data memory, printing the bar-code representation of a pro (screens) to cassette tape and a complete onscreen editor. Requires at least 16K of RAM. gram would necessarily entail manual translation. With $49.95 the system in its present configuration, bar-code output new! GRAPHICS ANIMATION by Lee Anders. This package provides the BASIC program from the printer does not seem to be practical, although it mer with a powerful set of commands for graphics and animation. The program is written in machine language but is loaded together with your BASIC program and graphics definitions is tantalizingly close. with a CLOAD command. Any image from a character to a large graphic shape may be plotted, moved, or erased with simple BASIC commands. Encounters of plotted character sets with background characters are detected and background images are preserved. Con tains a medium resolution plotting routine. A keyboard routine detects key presses without carriage returns. Includes a separate program for constructing images. $29.95 The mere possibility of obtaining new! STARBASE HYPERION™ by Don Ursem. At last a true strategic space game for the hard copy greatly enhances the Sorcerer! Defend a front-line Star Fortress against invasion forces of an alien empire. You create, deploy, and command entire ship squadrons as well as ground defenses in this complex tactical simulation of war in the far future. Written in BASIC and Z-80 code. Full utility of the calculator... graphics and realtime combat status display. Includes full instructions and STARCOM battle m a n u a l . R e q u i r e s a t l e a s t 1 6 K o f R A M . $ 1 7 . 9 5 new! HEAD-ON COLLISION"' by Lee Anders. You are driving clockwise and a computer- The Printer controlled car is driving counter clockwise. The computer's car is trying to hit you head on, but you can avoid a collision by changing lanes and adjusting your speed. At the same time The printer is easily the most engaging component of you try to drive over dots and diamonds to score points. Three levels of play, machine the HP-41C system. The mere possibility of obtaining language programming, and excellent graphics make this game challenging and exciting for a l l . A t F e a s t 1 6 K o f R A M i s r e q u i r e d . $ 1 4 . 9 5 hard copy greatly enhances the utility of the calculator, new! LUNAR MISSION by Lee Anders. Land your spacecraft softly on the moon by since it relieves the operator of the need to transcribe controlling your craft*s three propulsion engines. Avoid lunar craters and use your limited results as they become available. The printer for the HP- fuel sparingly. You can see both a profile view of the spacecraft coming down and a plan view of the landing area. Land successfully and you get to view an animated walk on the 41C does more than that: it will reproduce anything that moon. Nine levels of play provide a stiff challenge to the most skillful astronaut Requires at appears in the display and much else besides. l e a s t 1 6 K o f R A M . $ 1 4 . 9 5 The print mechanism is a thermal, dot-matrix one; new! HANGMAN/MASTERMIND by Charles Finch. Two traditional games are brought to life by Sorcerer graphics. HANGMAN has three different vocabulary levels for you to choose 24-character lines are printed on rolls of heat-sensitive from. I n MASTERMIND, the computer selects a four-character code and you have to uncover it. These two games provide an enjoyable way for young people to develop their vocabulary paper about 6 cm wide. There is a standard set of 127 and their logical reasoning ability. Written in BASIC. $11.95 characters, including full uppercase and lowercase alphabets, the ten numerals, a few Greek letters, and QS SMART TERMINAL by Bob Pierce. Convert your Sorcerer to a smart terminal. Used with a modem, this program provides the capability for you to communicate efficiently and save miscellaneous other symbols and punctuation marks. All connect time with larger computers and other microcomputers. The program formats characters can be printed in a standard 5 by 7 matrix or in incoming data from time-sharing systems such as The Source for the Sorcerer video. Incoming data can be stored (downloaded) into a file in RAM. Files, including programs, may a double-width format. A few of the standard calculator be saved to or loaded from cassette, listed on the video, transmitted out through your instructions trigger printing and, in addition, the printer modem, or edited with an onboard text editor. Interfaces with BASIC and the Word P r o c e s s o r P a c . $ 4 9 . 9 5 has its own repertoire of about twenty-five instructions. DPXra (Development Pac Extension) by Don Ursem. Serious Z80 program developers will Programs can be listed in their entirety, or a designated find this utility program to be invaluable. Move the line pointer upward. Locate a word or number of lines can be printed out; in either case, the symbol. Change a character string wherever it occurs. Simple commands allow you to jump directly from EDIT to MONITOR or DDT80 modes and automatically set up the I/O you want listing shows the same mnemonics that appear in the for listings. Built-in serial driver. Stop and restart listings. Abort assembly with the ESC key. Save backup files on tape at 1200 baud. Load and merge files from tape by file name. display. The path followed by the calculator through a Versions for 8K, 16K, 32K, and 48K Sorcerer all on one cassette. Requires the Sorcerer's program being executed can be traced, providing a record D e v e l o p m e n t P a c . $ 2 9 . 9 5 of all instructions and operands; this is a useful facility when the program does not function as expected. The Other utility programs: contents of the operand stack can be printed out with a PLOT by Vic Totomei. High res and tow res modes $14.95 SHAPE MAKER™ by Don Ursem. An on-screen character maker $14.95 single command; so can the contents of all allocated DEBUG by Bob Pierce. Debug machine language programs $14.95 SOFTWARE INTERNALS MANUAL by Vic Tolomei. A 64-page book $14.95 memory registers, or of a defined block of registers. In Other game programs: addition, assignments of nonstandard functions to the M A R T I A N I N V A D E R S ™ b y J a m e s A l b a n e s e $ 1 4 . 9 5 keyboard and the status of all flags can be listed. All of N I K E I r b y C h a r l e s F i n c h a n d B o b B r o f f e l $ 1 1 . 9 5 these functions can be executed manually or within a pro T A N K T R A P b y D o n U r s e m $ 1 1 . 9 5 M A G I C M A Z E " b y V i c T o l o m e i $ 1 1 . 9 5 gram. F A S T G A M M O N ™ b y B o b C h r i s t i a n s e n $ 1 9 . 9 5 The most commonly invoked print functions are those that print the contents of the X register (roughly QuaLrry software equivalent to an accumulator), the alpha register, or a 6660 Reseda Blvd.. Suite 105. Reseda. CA 91335 print buffer. The variations offered by these instructions Telephone 24 hours, seven days a week: (213) 344-6599 allow the output of a program to take almost any format within the physical capabilities of the printer. The main WHERE TO GET IT: Ask your nearest Sorcerer dealer to see Qualify Software's Sorcerer limitations are the time and space the programmer wishes Krograms.olders may Or, telephone if you prefer, their ordersyou may and order we will directly deduct from $ 1 us. from MasterCharge orders over $19 and to Visa compen card- to dedicate to format commands. It is easy to list a series sate for phone charges. Or mail your order to the address above. California residents add 6% sales tax. Sh/pp/ngCnarjres: Within North America orders must include $1.50 for first class of variable names, each followed by a colon or an equals shipping and handling. Outside North America the charge for airmail shipping and handling sign and a value. Tabulating two or three columns of is $5.00 — payable in U.S. currency. !The Rime "SORCERER" has been Iradenurked by Enidy. Inc. numbers so they line up vertically on their decimal points
126 Jtnuuy 1981 © BYTE Publications Inc Circle 77 on inquiry card. Circle 78 on Inquiry card. «^^^ demands a somewhat larger investment of program program called PRPLOT (print plot), which is committed memory and execution time. to read-only memory in the printer. When PRPLOT is ex The dot-matrix print head is a single vertical row of ecuted (see listing 1), it first asks the user to supply cer print elements that sweeps across the paper forming tain information that determines the form of the characters as a series of columns (see table la). A special graph, such as the range of x and y. It then calls on a set of printer instructions brings this process under pro named program, also supplied by the user, that for each gram control so that nonstandard characters can be given value of x must return a value f(x). The resulting created. Indeed, the printer reproduces any pattern that graphs cannot compare to the product of an x,y plotter, can be defined by a matrix 7 dots high and no more than but they can be run off quickly and are adequate for 40 dots wide. If the pattern fits in a 7 by 7 box, it can be gauging the basic form and range of a function. PRPLOT treated as a special character, stored in a register, and can also be executed from within a program without the called up as needed. In principle, a complete font could prompting for input values, and various parts of it can be be built up in this way, although its usefulness might be called independently. somewhat impaired by the limited capacity of the print buffer: only 6 special characters per line can be printed. A Programming with Labels more practical application is the creation of schematic An organizing principle of programs for the HP-41C is symbols and markers, such as playing-card suits, chess that all references and transfers of control are made by pieces, or the phases of the moon (see table lb). means of labels. The name given to a program constitutes Another capability of the printer is the plotting of a global label, one that can be accessed from any point in graphs for any function that can be expressed in the form program memory. By invoking the name, a program can y = f(x). The graph is drawn under the direction of a be called as a subroutine and can even call itself, although there are limits to such recursion. Labels within programs are generally local, so that the same labels can be repeated in different programs without (a) (b) interference. Subroutine calls and branches can be made STANDARD CHARACTERS SPECIAL CHARACTERS only to a label; there is no absolute addressing by line number. As a result, all programs and procedures within X X X X * * * ♦+ i * V "A" 9 > ? ? 9 @ 2-digit number that follows is interpreted as the register A P B B C C D D where the subroutine name or label will be found. Any E E F F G G H H I I J J K K L L register, including those of the stack, can hold the in M M N N 0 0 P P direct address. Subroutines can be nested six levels deep Q Q R R S S T T before the return address of the highest-level routine is U U V V U U X X lost. Y Y Z Z [ C \ \ f T Conditional tests of numerical data include various ] 3 t t _ _ combinations of 'less than," "greater than," "equal to," a a b b c c d d e e f f 9 <3 h h and "not equal to"; alphabetic strings can also be com i i j J k k 1 1 pared, but only for equivalence. All the tests have the n n n n 0 o p p same format, in which a false result causes the instruction 4 <*. r r s s t t following the test to be skipped. Tests of flags (set or u u V V y w X X clear) employ the same scheme. The complement of fifty- y y z z t T f 1 1 •» -> Z Z I" h six flags seems particularly generous. Eleven flags are completely unencumbered for use in programs; the rest Table 1: Character set as printed by the HP-41C printer. The control the status of the HP-41C and its peripherals, standard character set, shown in table la, contains 127 let thereby affording the calculator a valuable amount of ters, numbers, and other symbols. About sixty of them, in- self-knowledge. eluding the full uppercase alphabet, can also be represented in a somewhat different form in the display of the HP-41C Loops itself. Each character can be printed in a standard 5 by 7 dot The control of loops in HP-41C programs is facilitated matrix or in a double-width format. Special characters (table lb) can also be created by specifying the pattern of dots in by two instructions that store all the heeded information each column of the character. in a single register. The instructions, ISG (increment, skip if greater) and DSE (decrement, skip if equal), refer
128 January 1981 © BYTE Publication* Inc Circle 79 on inquiry card. directly or indirectly to a register holding a number of the The main program in CHART (listing 2), which is con form nnnnn.tttcc. Here nnnnn is the number to be tested, fined to the first 20 lines, is little more than a list of XEQ ttt is the value against which it is tested, and cc is the statements. It first prompts the user for needed informa amount by which nnnnn is incremented, or decremented. tion, then does some preliminary calculations and prints The compacted form is a convenience, although I find it a header that will identify the graph. An external pro odd that the incremented number has a range of up to gram (see listing 4) is then called once for each bar; it is 99,999, whereas a jump must take place whenever it ex expected to return a value defining the length of the bar ceeds 999. and a label of not more than 4 characters. It is worth noting that the actual calculation of the bar Other Programming Features length is a trivial operation. The bulk of the program is The HP-41C cannot realistically be said to support taken up with input and output routines, which are in structured programming, not as I understand the term. tended to minimize the burden on the user's memory and The rule that all procedures should have a single entry faculties of interpretation. A bar graph generated by the point and a single exit, which is one of the precepts of CHART program is shown for data on the distribution of structured programming, cannot be observed without ex digits obtained from the RDM LN pseudorandom- treme awkwardness. On the other hand, the program- number generator; see listing 5. control structures of the HP-41C strongly encourage the composition of modular programs, where each procedure Next Generations is a self-contained unit, small enough to be fully What more can one ask for in a programmable understood and capable of being tested independently. In calculator? Quite a lot; there is much to look forward to a program longer than a few hundred lines, some such in the next generation. More memory is always near the technique for imposing order is obligatory. top of such a wish list. One way of supplying it, which In the end, the capabilities of the HP-41C can be ex might be compatible with the present mainframe, would hibited best by real programs and their output. A few be in a double-density memory module. The entire ad short utility routines and a longer program, called dress space could then be utilized without filling all the CHART, are given in listings 2 and 3. CHART, which in ports. cidentally shows off to good advantage the versatility of The very existence of ports inspires thoughts of other the printer, produces a bar graph, a form of display that Text continued on page 136 is more appropriate for some kinds of data than the line graphs of PRPLOT. Listing 1: Graph of the function (sin x)/x was drawn by PRPLOT, a program that resides in read-only memory in the HP-41C printer. The function itself is defined by a separate pro At last—lhg gram (at bottom), which evaluates the expression each time it is supplied with a value of x and called PRPLOT.
PLOT OF SIN/X Typewriter Interface! X
130 January 1981 © BYTE Publication* Inc Circle 80 on inquiry card. Listing 2: A bar-graph program. CHART, the HP-41C program for generating bar graphs, is written as a series of modules. The first of these prompts the user to supply certain initial information that will determine the form of the graph. An alternative entry point, CHARTP, is intended for occasions when the bar-graph routine is called from another program; this entry point bypasses the prompting. For each bar drawn, CHART calls on a user-supplied program, which must return two items, the value to be plotted in the X register and a label for the bar no more than 4 characters long in the alpha register. The bar is actually formed in subroutine 08 out of a standard character and additional print columns for fine adjustment of the length.
814LBL "CHART* 61 RCL 15 117 ADV 92+LBL a 62 XEQ 18 118 RTN 03 XEQ 88 Initialization; can 63 STO 17 84*LBL !CHARTP" 64 5 be executed from Calculate absolute 85 XEQ 81 the keyboard by 65 XOY 66 X<=Y? position of axis; 86 XEQ 82 pressing "A." if beyond the range 87 XEQ "BAR" 67 ST- 17 of the graph, axis 119*LBL 85 98+LBL A 68 132 is suppressed. 128 8 89XEQ 83 69 XOY 121 STO 18 18XEQ 84 78 X>Y? 122 RCL 17 11 XEQ 85 Main calculation and 71 ST- 17 123 X=8? 12»LBL 38 printing of bars. Calls 72 RTN 124 RTN 13XEQ 87 a user program whose 125 119 14RCL 18 name is stored in 126ACCOL 15 INT register 11. 127 RDN 16XEQ IND 11 128 RCL 15 17XEQ 88 73+LBL 82 129 XEQ 11 18 ISG 18 74ADV 138 ST* 18 19CTO 38 75ADV 131 2 28XEQ 87 76 "P" 132 / 21GTO 58 77ACA 133 - Labels axis 78 SF 13 134 5 within graph, Print identifying if it has not 79 "LOT OF 135 X>Y? 88ACA been suppressed. "Plot of 'PGM NAME' 136 GTO 52 81 CF 13 137 RDN 22«'lBL 88 82 SF 12 138 132 23 CF 23 83 RCL 11 139 RCL 18 24 "PGN NAHE?' 84ACX 148 - 25AON 85 CF 12 141 X 183«LBL 84 48*LBL 81 184 RCL 13 168+LBL 88 49 RCL 12 185ACX 161ACA Set up register 162 3 58 1 for looped calls 186 XEQ 11 51 - to user program. 187 STO 18 163 SKPCOL 52 1 E3 188 RCL 14 164-RDN Master subroutine for accumulating and 53/ 169 XEQ 11 Labels extrema 165 XEQ 18 118 ST* 18 166 X<=8? printing a bar. Checks 54 STO 18 of Y axis. if the length is zero; 55 137 111.144 167 GTO 87 112 RCL 18 168 127 if so, executes LBL 07. 56 RCL 14 Checks if the length is 57 RCL 13 Calculate coefficient 113 - 169ACCOL 58 - relating Y-axis 114 SKPCOL 178 RDN 59 / scale to graph width 115 RCL 14 171 136 68'STO 16 of 137 columns. 116 ACX Listing 2 continued on page 134 132 January 1981 © BYTE Publication* Inc 239+LBL 18 Listing 2 continued 294»LBL 16 248 RCL 13 172 X<=Y? greater than the maximum; 285 1 173 GTO 99 296 X>Y? 241 - if so, executes LBL 09. 242 RCL 16 174 RBH Otherwise, the bar is 297 RTN Calculates the length 175 STO 19 298 X=Y? 243 * of the bar. built up by LBL 15 244 FIX 8 176 XEQ 15 and LBL 16. 299 RTN 177RDH 219 42 245 RND 178 XEQ 16 Finishes a bar by 246 FIX 2 211 fiCCCL 247 RTN 179 127 212 RDH accumulating individual columns until actual 189ACCOL 213*- 248+LBL 11 181 XEQ 17 214 1 length equals specified 249 ABS 182 XEQ 12 215 X>Y? length. 259 SF 25 183 RTN 216 RTN 251 LOG 217 X=Y? 252 CF 25 Calculates width of 218 RTN a number (eg: axis or 184*LBL 89 253 INT 219 85 254 5 extrema labels) in number 185 STO 18 228 fiCCOL of columns. 186 XEQ 15 255 + Special routine for 221 RDN 256.7 187RDN a bar that must fill 222 - 188 XEQ 16 257 * the entire width of 223 GTO 16 258 RTN 189 127 the graph. 198 fiCCOL 224*LBL 17 259*LBL 12 191ADV 269 135 192 RTN 225 RCL 18 226 1 261 RCL 19 Adds space to fill out a 227 + 262 - line, other than a line with 193»LBL 15 228 RCL 17 263 SKPCOL a bar, then prints a Y - 194 7 229 X*8? Inserts space from 264 119 maximum marker. 195 X>Y? 238 X<=Y? end of bar to maximum 265 ACCOL 196 RTN Accumulates the maximum 231 RTN then adds a marker for 266 ADV 197 X=Y? integer number of gray-tone maximum Y 267 RTN characters (standard char 232 STO 18 198 RTN 233 XOY 199 31 acter 31) that will fit in the bar. 234 - 268»LBL 58 298 fiCCHR 235 SKPCOL 269 ADV 291 RDN 236 119 278 ADV Beeps to mark finish. 292 - 237 ACCOL 271 BEEP 283 GTO 15 238 RTN 272 END E RACET SORTS — RACET UTILITIES — RACET computes — RACET SORTS — RACET UTILITIES — RACET computes — RACET SORTS — RACET UTILITIES — RACET computes — U 2 HARD DISK MULTIPLEXOR BASIC CROSS REFERENCE UTILITY (Mod II64K) $50.00 g FOR THE TRS-80* Mod II SEEK and FIND functions for Variables, Line Numbers, Strings, Keywords. 'All' 3 NOW YOU CAN HAVE THAT LARGE COMMON DATA BASEII options available for line numbers and variables. 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XCOPY provides multi-file copies, 'Wild-card' mask select, absolute § utility Includes options for specifying sectors/gran, platters/drive, logical sector mode and other features. SUPERZAP allows examine/change any sector on f disk siz6 otc diskette include track-0, and absolute disk backup/copy with I/O recovery. DCS a HARD DISKDRIVE 4 CONTROLLER $5995 RACET HSD Software $400 builds consolidated directories from multiple diskettes into a single display or 5 Call for multiuser pricing. Dealers call for OEM pricing. listing sorted by disk name or file name plus more. Change Disk ID with DISKID. 2] XCREATE preat[locates files and sets 'LOF to end to speed disk accesses. DEBUGII BASIC LINK FACILITY 'BUNK' $25 Mod I, $50 Mod II adds single step, trace, subroutine calling, program looping, dynamic disassembly Link from one BASIC program to another saving all variables! The new program a n d m o r e ! ! a can be smaller or larger than the original program in memory. The chained program may either replace the original program, or can be merged by statement number. D E V E L O P M E N T PA C K A G E ( M o d I I 6 4 K ) $ 1 2 5 . 0 0 ' The statement number where the chained program execution is to begin may be Includes RACET machine language SUPERZAP, Apparat Disassembler, and Model > s p e c i fi e d ! ( M o d I M i n 3 2 K 1 - d i s k ) II Interface to the Microsoft 'Editor Assembler Plus' software package including § uploading services and patches for Disk I/O. Purchase price Includes complete c I N F I N I T E B A S I C ( M o d I Ta p e o r D i s k ) $ 4 9 . 9 5 copy of Editor Assembler + and documentation for Mod I. Assemble directly into | Extends Level II BASIC with complete MATRIX functions and 50 more string memory, MACRO facility, save all or portions of source to disk, dynamic debug 3 functions. Includes RACET machine language sorts! Sort 1000 elements in 9 f a c i l i t y ( Z B U G ) , e x t e n d e d e d i t o r c o m m a n d s . 5 seconds!! Select only functions you want to optimize memory usage. C O M P R O C ( M o d I — D i s k o n l y ) $ 1 9 . 9 5 I INFINITE BUSINESS (Requires Infinite BASIC) $29.95 Command Processor. Auto your disk to perform any sequence of instructions that 5 Complete printer pagination controls — auto headers, footers, page numbers. you can give from the keyboard. DIR, FREE, pause, wait for user input, BASIC, No. 8 Packed decimal arithmetic — 127 digit accuracy +, -, *, /. Binary search of FILES and MEM SIZE, RUN program, respond to input statements, BREAK, „ of sorted and unsorted arrays. Hash codes. return to DOS, etc. Includes lowercase driver, denounce, screenprint! | CHECK, VISA, M/C. C.O.D.. PURCHASE ORDER •TRS-80 IS A REGISTERED TRADEMARK TELEPHONE ORDERS ACCEPTED (714)637-5018 OF TANDY CORPORATION Ir* RACET computes -g 702 Palmdale, Orange, CA 92665 £!!! RACET !!! SORTS !!! !!!— RACET !!! UTILITIES !!! !!! — !!! RACET• !! !!!computes !!! — !!! RACET !!! SORTS !!! —!!! RACET !!! UTILITIES !!! !!! — !!! RACET !!! computes !!! !!! — RACET !!! !!! SORTSt^H r^BB ^mm —M RACET!!! MM UTILITIESBBB ^H ^M IBM —!!! RACET !!! computes !!! !!! — *< m 134 January 1901 © BYTE Publications Inc Circle 83 on Inquiry card. Circle 84 on inquiry card. Text continued from page 130: to give results accurate to more than seven or eight peripheral devices. A cassette recorder could provide decimal places. mass storage and would make feasible operations on Actually, a subsidiary problem is more serious than large blocks of data. An x,y plotter could be driven very that. Conditional tests on data are carried out on the full efficiently by the HP-41C, albeit at a leisurely pace. With 10-digit representation. Consequently, a test that effec a fairly simple interface, it should be possible to connect tively asks 'Is (V2)2 equal to 27" will give a false result, the calculator to a computer system. The likelihood that which can lead a program far astray. any of these products will ever be forthcoming is un known. It is probably too much to ask that Hewlett- Listing 3: Utility routines for the HP-41C. These two routines Packard release technical information on the signals are the kinds of programs that can remain in memory as available at the ports so that others could develop plug- resources to be drawn on by other programs, somewhat like compatible devices. Some intrepid experimenter with a macro instructions in an assembly language. BAR simply prints logic probe may do it anyway. a heavy bar across the width of the paper to separate different There are a few gaps in the instruction set of the HP- kinds of information. TAB handles the spacing of numbers to be 41C that should not be perpetuated in future calculators. printed in vertical columns. It must be supplied with the number For example, there are tests for x < y, for x ^ y and for to be printed (in the X register) and the number of character x > y, but there is no test for x ^ y. Of course, any spaces to be measured from the present position in the line of print to the decimal point. TAB was employed in formatting the desired logic function can be fabricated out of the existing random-number data in listing 2. instructions, but the programmer should not have to go to that trouble and should not have to remember which 81»LBL "BflR" 81M.BL 'TAB' of the tests is the missing one. 8 2 A D V 8 2 A S S The most fundamental defect in the architecture of the 8 3 . 8 2 3 8 3 S F 2 5 8 4 3 1 8 4 L O G HP-41C, inadequate numerical precision, is a serious 8 5 » L B L 8 1 8 5 C F 2 5 flaw indeed. Numbers are represented, both internally 8 6 A C C H R 8 6 X < = 8 ? and in the display, with 10 decimal digits; there are no 8 7 I S G Y 8 7 C L X guard digits. As a result, inaccuracies are quite often in 8 8 G T O 8 1 8 8 I N T troduced into the least-significant digit. For example, 8 9 F ' R B U F 8 9 1 (V2)2 is evaluated by the calculator as 1.999999999. For 1 8 A D V 1 8 + 1 1 A D V 1 1 R C L X operations on some data, the corruption goes still deeper 1 2 E N D 1 2 3 . 1 and 2 or 3 digits become suspect. There is something ab 13 / surd about the world's fanciest calculator not being able 14 INT 15 + 16CHS 17 t 18SKPCHR 19END Listing 4: Random-number routines for the HP-41C. These two random-number generators, standard coding exercises for pro grammable calculators, both calculate a pseudorandom real value, then select a single pseudorandom digit for return to the calling program. RDM LC employs the standard linear- congruential method, which has virtues and failings that are well understood. In this example, RH* lis equal to [24,298RH + 99,991\mod 199,017- RDM LN is an algorithm the author stumbled upon but has NOW. . .Continuous Checks not seen in the literature. R„ ♦ , is defined as 1/ln RH. Experimen That Can be Used With or Without Your Computer/1 tal runs of up to several thousand iterations have given good The Best in A Home Checking System results, but the behavior of the algorithm is not understood. A That's right. Continuous Checks in a 3-to-a-page UNIQUE sample test is shown in listing 5. desk sat design that can be computer printed or You won't find checks like these at any bank or handwritten - just as you now do your present forms company. Even so, our special small home checks. quantity printing process will give you quality BULBL "RDM LN" 8ULBL "RDH LC" VERSATILE and appearance equal to any check supplier. 82 RCL 28 82 RCL 28 Our checks are not a high-volume business form Color co-ordinated imprinting is standard on adaptation. They're especially designed for the blue. grey, tan, or green checks. 83 ABS 83 24298 home or low volume user. Now. you don't have Standard imprinting and encoding is as shown 84 LN 84 * to change your check writing habits just to use above (logos and multi-color printing are 85 1/X your computer. optional). 85 99991 THOUGHTFUL FEATURES Our prices are reasonable too. Two Hundred 86 STO 28 86 + chocks are just $29.95 (envelopes 511.95). Programming? Easy. All stub and check informa 87 1 E3 Five Hundred checks are $49.95 (envelopes 87 199817 tion is on the same line. No need to change 923.95). Data Ring Checkbooks are only $5.95. tractor width either. Our checks are standard 88 * 88 MOD 9V4" width for tractor feed printers. Special "ORDER NOW" Offer 89 FRC 89 STO 28 If you order now. we'll sond you a checkbook COMPLETE HOME SYSTEM FREE. You'll save $5.95. Just enclose a voided 18 18 18 1 E3 When you've finished printing your monthly check (for encoding information) with your 11 * 11 / checks on your computer, store your checks and payment. (VISA - MasterChargo orders must stubs in our attractive Data Ring Binder Check show signature, expiration date, end account 12 INT 12 FRC book. Later, if you have a few checks to write number). Or. send today for samples (sorry, we 13 ABS 13 18 there's no need to load them into a printer - just can't make this free offer on requests for write a check right there at your desk as shown samples) To: 14 END 14 * above. 15 INT And, you can mail your checks in our dual SYNERGETIC 4715 SHEPHERD RD. windowed envelopes to eliminate addressing MULBERRY, FL 16 END chores. SOLUTIONS 136 January 1981 © BYTE Publications Inc Circle 85 on Inquiry card. Listing 5: Bar-graph results of the CHART program, given in listing 2. The graph represents pictorially the distribution of the 10 digits in a sample of 2500 pseudorandom numbers. The numbers were generated by another program, RDM LN (shown WE in listing 4), with the bookkeeping done by a third program. Te s t o f " R D M L N " Plot of "RRNDOM" vSV/ DELIVER! Hunber of trials 2586 fiilillSilSillliillHSSi •>Jk4 n VANDAIA yjB| . CP/M* js a registered trademark ol Oigltal Research. significant that the inability of a calculator to alter its hS^h, TRS-80* is a registered trademark of Radio Shack, Inc. own instructions is what most clearly distinguishes calculators from computers. ! 138 January 1981 © BYTE Publications Inc Circle 88 on inquiry card.