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An introduction to Creed teleprinters and punched paper tape equipment An introduction to Creed teleprinters and punched paper tape equipment

CONTENTS

Introduction

What is a teleprinter?- The teleprinter code 2

Start/stop principle- Telegraph signals 3

Telegraph speed- Outline description of a teleprinter- Stages of transmission 4

Keyboard - Receiver 5

Punched tape technique- Kinds of punched tape- Methods of coding information on punched tape 6

Applications to digital computers­ Input preparation- Manual tape preparation- Tape editing 10

Output recording and printing­ Model Seventy-five interpreter set­ Model Seventy-five 5-wire reproducer set 11

The equipment- A short introduction to each of the major Creed machines 12

Glossary of terms 16 INTRODUCTION Creed teleprinters and punched paper tape equipment were originally devel­ oped for use in the telegraph com­ munication field and they have been increasingly used ever since in telegraph systems all over the world. During recent years, however, their use has been extended beyond this traditional field to a rapidly growing number of non-telegraphic applica­ tions such as the provision of input and output facilities for digital com­ puters and the automation of existing systems such as punched card accounting and mechanised addressing. As a result of this sudden increase in the number of applications that are being found for teleprinters and punched tape, considerable interest has been shown in this equipment by engineers and others who wish to discover whether it can be applied to their own special problems. This bulletin has been written princi­ pally for such readers and others who need to know of the basic principles used in teleprinter communications systems. It contains a brief, non­ technical introduction to the general principles underlying the operation of Creed teleprinters and punched tape equipment, and includes a brief description of each of the various machines available. It must be emphasised that this bulletin does not describe all the non­ telegraphic applications that have been made to date of this equipment, nor does it contain any engineering details of circuits or machines. Full technical details and free advice on how any Creed equipment can be used in telegraph or data processing systems is available on request. Any system for transmitting and re­ nsmission of 1. Run-Out Key. The deprdssion of ceiving messages electrically over a paper on the this key results in the last signal sent distance in the form of coded signals to be fed up to being repeatedly transmitted for as is called a telegraph system. rec~ived message long as the key remains depressed. If the messages are automatically is printo A!-Tn..-.....m;;~ e 'Line Feed' 2. 'Here is' Key. The depression of printed by the receiving apparatus, the function is not, of course, used). this key causes the key oard trans­ system i;> then r'eferred to as a printing 2. Carriage Return. This function mitter to send automatically the calling telegraph system. causes the carriage on the receiving station's identifica ron code signal to The teleprinter is the basic piece of teleprinter to return to the beginning the called station. equipment of the Creed printing tele­ of its travel so that the printing starts graph system. It consists of two parts: again at the beginning of a line. THE TELEPRINTER a keyboard transmitter and a receiver. (Again, with ta e print:ng, this is CODE not used). The ltelegraphy. The method of of characters, numerals, signs and that the whole message has been code allocation indicated in Fig. 4 is functions. The most commonly used received. the CCITT International Code No. 2, items of intelligence are shown in the 4. Bell. The transmission of this which is the one at present in general three typical keyboard layouts function causes a bell to ring (or pro­ use. illustrated in figs. 1 - 3. duces some other warning indication) It will be noticed that the two kinds of The characters in all three layouts are at the called station to attract the elements of the code are called 'mark' the twenty-six letters of the English operator's attention. and 'space' elements. These terms alphabet. While this is the most 5. Space. This is similar to the were derived from telegraph systems common arrangement, layouts for normal spacing tunction on a type­ employing the Morse Code, where the other alphabets with more or less than writer. Its transmission results in the dots and dashes were referred to as twenty-six letters are available. carriage on the receiving teleprinter 'marks' and the spaces between the Similarly, althoud'h the numerals in feeding along one space without dots and dashes simply as 'spaces'. these layouts are confined to 0 and printing. In connection with the 5-unit code these meanings are, of course, irrele­ 1 - 9, these may be augmented by 6. Letters and fractions. vant, but the terms have been adopted 1. Figures. These functions have a as convenient labels for distinguishing Signs such as'%','@' and'?', may purpose which will be explained in the between the two kinds of elements of also be varied to suit special require­ next section. the code. A 'mark' element may be ments, such as data processing In the keyboard layouts in Figs. 1 - 3, defined, therefore, in terms of the instructions or weather charts. two keys ('Run Out' and 'Here is') International Code as any element of Seven functions are controlled from have not so tar been referred the code represented by a solid dot in the keyboard. They are Line Feed, to, since they are not strictly speaking Fig. 3; similarly, a 'space' element is Carriage Return, Who-are-You?, Bell, items of intelligence, i.e. no code Space, Letters and Figures. The signal is allocated to them. Their purpose of these functions is as purpose is as follows: follows:

2

TELEGRAPH SPEED OUTLINE DESCRIPTION STAGES OF The unit of telegraph speed is called OF A TELEPRINTER TRANSMISSION the 'baud', after the famous French The basic elements of a simple point­ There are a number of well-defined telegraph inventor Baudot. It is equal to-point teleprinter system are stages and processes between the to the number of shortest telegraph represented in Fig. 5. depression of a key and the impres­ signals, i.e. units, per second. The transmitter consists essentially of sion of the selected character on the The present international standard is a metal tongue T which, when a key is paper in the distant printer. These are 50 bauds, which makes the unit equal depressed, is caused to move between shown schematically in Fig. 7 which, to 20 milliseconds. With 7!-unit trans­ two contacts M (mark) and S (space) for clarity, represents the stages for mission, the 'Start' signal and the five in a manner determined by the code the transmission of a particular letter code signals are, therefore, each 20 combination of the key depressed. -A, for a double-current teleprinter. milliseconds in length while the 'Stop' Voltages of opposite polarity are These general principles apply to all signal is 30 milliseconds, and the connected to the two contacts and the conventional teieprinters now in transmission time for a complete 7!­ tongue is connected to the line. production, but the means of achieving unit transmission is 150 milliseconds, the same end result vary quite The basic element of the receiver considerably from model to model. equal to 6·6 characters per second. consists merely of an electromagnet, Another way of measuring telegraph one side of which is connected to line For this reason it is not possible to speed, which is very useful, is in words and the other side to earth. describe here in detail the sequence of operations between the depression of per minute. In order to obtain a word­ Thus, when a key is depressed, a measure, five letters and a space are a key and the printing of a character on sequence of square-wave pulses the distant teleprinter. The following taken to be the average length of a (ignoring distortions caused by the stages, however, apply to all current word in English, i.e. six code trans­ line constants and the electromagnet missions. A telegraph speed of 50 models whether the printing unit is a inductance) is transmitted to the moving type-bobbin (Model Seventy­ bauds, using 7!-unit transmission, is electromagnet, the armature of which five), a moving type-basket (Model thus equivalent to is caused to reproduce the movements 444) or a stationary typewheel with a 1000 60 . of the transmitter tongue. The fSO x =66-t wordsjm1n. moving carriage (Models 7, 8 and 54). 6 remainder of the receiver translates the code combinations to produce 1 Key is depressed. the desired functions. 2 Code is set up on keyboard coding The method of transmission repre­ unit. sented in Fig. 5, in which the pulses of 3 Transmitter unit 'reads' off code set transmitted voltage are of opposite up on coding unit. polarity, is called 'double-current' 4 Tongue of transmitter is moved operation. Although in the figure the between two contacts (positive and marking voltages are negative and the negative battery) in accordance with spacing positive, there is no rule that the code for the character to be is universally followed. The G. P.O., for transmitted. example, adopt the convention in 5 Transmitter automatically inserts Fig. 5, whereas America and the Start signal followed by a combination continental countries adopt the of five marks or spaces (negative or reverse convention. positive battery) and a Stop signal Fig. 6 illustrates the 'single-current' to line. method of operation, in which voltage 6Signal is received, and fed to electro­ is applied only to one contact. In this magnet of distant teleprinter. system, a spring is used to return the electromagnet armature when there is 7 Electromagnet armature moves back no current flowing through the electro­ and forth in accordance with code of magnet. Once again, no set rule is character being transmitted. followed in deciding whether the 8 Code is transferred to mechanical voltage should be applied to the store. marking or spacing contact or whether 9 Receive mechanism reads off code this should be positive or negative. and positions appropriate type against printing point. 10 Character is printed. 4

senting each item of information by a Computer codes, like the ordinary 2. The decimal digits, together with series of punched holes in one of the teleprinter code, follow the principle of the most important arithmetical five code tracks (see Fig. 12). A sixth disjunctive coding, but the items of symbols and teleprinter functions, ar-e item of information, if this is a con­ information are allocated to the differ­ coded by combinations having an odd tinually repeated item such as a fixed ent code combinFttions in such a way number of holes. This provides a very lapse of time or a fixed distance, can as to simplify the detection of errors useful safeguard against the most be represented by using the feed holes and to satisfy other operating common teleprinter faults, viz. the for the purpose. Various methods may requirements. substitution of a mark for a space be employed to increase the number A detailed discussion of this subject ('extra') and of a space for a mark of conjunctive items of information cannot be given here, but the main ('failure'). When either of these faults that may be coded. For example, nine requirements for a good computer occurs in a combination having an odd sources of information may be coded code can be seen from a study of number of holes, it always turns into by using four of the code tracks for Fig.15, which gives the code employed one with an even number. Hence, the eight items of information, the items by a leading computer manufacturer. items of information whose combina­ being punched in two successive tions have an odd number of holes It will be noticed in the first place that groups of four, and the feed holes cannot be changed into other items of the combinations are listed in order of used to represent time or distance as the group, but only into some other their equivalent numerical values, before. The fifth track is reserved for more easily detected items. 'holes' being taken to represent the 1 's discriminating between the first and and 'no-holes' the O's of binary This odd-parity condition leaves scope second group (see Fig. 13). This numbers. The convention is adopted for imposing a further condition on the method of coding may be extended to that the first teleprinter element of allocation of code combinations to the code 13, 17, etc. items of information, each code combination corresponds decimal digits. Since there are only with a corresponding reduction in to the least significant digit of the ten decimal digits, they may be coded the speed of recording as the number associated binary number. Thus, the by the first four significant digits of the of items increases. combination MSMMS corresponds to corresponding binary numbers, the To code mixed information, the most the binary number 01101. fifth significant digit being disregard­ straightforward method is to separate ed. Thus '0' is coded by '10000', '1' by The letters case contains the alpha­ the information into its disjunctive and '00001', '2' by '00010', '3' by '10011' and bet, full-stop, question mark, pounds conjunctive parts and use a mixture of so on. When such combinations pass sign and erase sign. The figures case the coding procedures already des­ into the computer, they are first contains the decimal digits, a number cribed for these kinds of information. checked for odd-parity and then the of arithmetical symbols, a range of Thus, the first two tracks could be fifth significant digit is ignored. programming symbols, the full-stop­ utilised for coding three disjunctive which is used for the decimal point­ 3. Erase is coded by five holes, i.e. the items of information using a 2-unit the erase sign and space. The figures all-marking combination. Punching code, and the remaining three tracks and letters case-shift functions appear errors are eradicated by overpunching utilised for three conjunctive items of in both cases as with the International with the erase combination. When this information. The feed holes could be Alphabet No. 2 (see Fig. 4) and for the combination is fed into the computer, used, as before, to represent time or same reasons. it is ignored. distance (see Fig. 14). The allocation of code combinations 4. The figure-shift signal is coded by In the foregoing discussion only a to these 61 characters and functions is blank tape, i.e. by an all-spacing small selection of the possible carried out in the following way: combination, so that on input the methods of coding information for blank tape before the perforations 1. The twenty-six letters of the alpha­ automatic data recording systems has automatically sets the computer into bet are coded by assigning to them the been given, and these have all been an assigned condition. based on the use of 5-unit tape. combinations whose numerical Considerably more information may be equivalents correspond to their posi­ coded by the use of 6-, 7- and 8-unit tions in the alphabet. Thus, 'V' which equipment. The principles of coding is the twenty-second letter of the on such equipment, however, are the alphabet, is coded by 10110 (i.e. same as those given above. SMMSM), the binary equivalent of 22. The object of this is to simplify alphabetical sorting.

8 T A E r-- --. - B (~ F r~A i 1:• 1. :• :·~~~-:~·~ 41 -\•1 el ~ ~·: :~ 1•1 !~: I I 11 I 1 I I 1e 1e lleeje •:••:··:··1 e 1 I I I 1e 14 I I• •: • •I• •t• •I• •1• •I• •: • •'• • 1• •I• •t• •'• •1• •: • .; • •:• .: • •: • •! PROCESS 'A' PROCESS 'E' I 1. 1e 1e ~~ .I .I .I ~ ·~··~··~·-'~·I I I I 1 1 1 • • I I 1e 14 I I 4 I .I .I .I e' .I .I e1 ~ ••••I - ~ PROCESS 'B' PROCESS 'F' \ I I. 14 !4 I. I. :• I I. I. I. I I. :. :• :· :. I. 1 • • ~ 'T' TIME BASE • • TIME BASE'T' PROCESS 'C' • • PROCESS'G' ~c- ... f-----c- PROCESS 'D' PROCESS'H' DH - • • 'DH' Dl SCRIMINATOR HOLES. G f+-o- ~0- Fig. 13 Conjunctive coding- second method H ..

FIGURES LETTERS BINARY DECIMAL TAPE A B c A c B CASE CASE VALUE VALUE 5 4 3 2 I FIGURES SHIFT • 0 0 I A • I I 2 B •• • 10 2 c ••• II 3 ••••• *4 0 100 4 ...... ••• • •••••• ( E •• 101 5 ) •• F • •• • 110 6 7 G Ill 7 8 H ••••• 1000 8 t I • • 1001 9 = J • • 1010 10 - K • •• 10 II I I v L • ••• 1100 12 L F M ••• II 0 I 13 p ••• s N • 1110 14 0 •••• 1111 ' I 5 0 p •••••• 10000 16 Q • 10001 17 F F > • • • ~ R •• 10010 18 3 s • ••• I 00 II 19 - T •• 10100 20 PROCESS 5 u • 1010 I 21 A B C 6 v • •• • lOll 0 22 I 'W • ••• lOIII 23 X X • •••• 11000 24 DISJUNCTIVE • y •• INFORMATION • 9 • 11001 25 (TWO-UNIT {: + z •• • II 010 2 6 CODE) • LETTERS SHIFT •• •• 1101 I 27 TIME BASE'T' • • • • • •• ••• 11100 2 8 ? •••• CONJUNCTIVE {. PROCESS 'D' n Ill 0 I 29 INFORMATION • C.R ( •••• • 11110 3 0 (ONE-UNIT PROCESS 'E' ERASE ERASE ••••• IIIII 3 I CODE) • •••••• PROCESS 'F' Fig. 14 MIXl'd COclillQ Fig. 15 A lyp1cal computer input-output code

9

The equipment

The following are the main products TELEPRINTER TELEPRINTER in the current Creed range. Ancillary MODEL 444 MODEL SEVENTY-FIVE equipment which has not been The Model 444 is a heavy duty page The Model Seventy-five is a high covered in this brochure includes performance page printer for use in high speed tape winders, tele- printing teleprinter which operates at up to 75 bauds, is compatible communications and data processing printer desks and pedestals systems. It is capable of operating at complete with power and signalling with all other current machines and is available with a full range of up to 100 words per minute and is voltage supply and control units, a optional extras and special facilities. available as a transmitter/receiver or hand correction unit for paper tape, a as a receiver-only. range of signalling rectifiers, a tele­ The 444 tape punching and reading printer page winder and edge-punched units are fitted as an integral part A feature of the machine is the card readers and punches. Creed also of the keyboard and not attached to the stationery platen and moving typehead supply custom-built consoles and side of the receiver. This brings which traverses across the width of switching equipment to meet specific increased operator convenience and the paper. This method of printing customer requirements. makes possible faster tape handling. means that the Seventy-five is un­ affected by tilting, shock or vibration, Another innovation in the 444, which and every character is visible as soon is the latest addition to the Creed as printed. range, is a Code Recognition Unit Important optional extras include (stunt box). This permits a wide attachments for tape punching and/or variety of remote control operations reading 5-unit tape. The punch which which can be used both within the operates simultaneously with normal machine for controlling the facilities of page printing can be switched in to the 444 itself and externally for switch­ punch tape from incoming signals or ing and other purposes. Thus it is from manual operation of the local possible to transmit a signal to a keyboard. The tape reading attach­ distant teleprinter which, when ment permits the automatic transmis­ received, will cause the unit to sion of pre-punched message tape at switch the tape punch on ready to up to three times the speed averaged reperforate an incoming message. in manual operation. Similarly it can be arranged to switch on an ancillary piece of equipment Other optional extras include: two­ (another teleprinter or tape punch) colour printing, operation counter, by the transmission of a special combined carriage-return/line-feed code. key, automatic carriage-return and line-feed action at end of line, 20- This new teleprinter has all of the character answer-back for keyboard facilities of existing equipment and and receiver-only models, dual-speed operates at any speed up to 100 words gear box, dual purpose friction/ per minute without the usually attend­ sprocket feed platen. ant higher fault rate and maintenance Specials include machines for auto­ requirement. matic regeneration of received signals; sequential to parallel, parallel to sequential conversion, 11! ch/sec. print out from parallel input, edge punched card printing-punching version, solenoid-operated case-shift (inversion), two-colour printing, keyboard inhibition, reperforator inhibition and tape reader trip, combined sequential/parallel output for combination recognition and switching, half-width platens for paper economy, high-speed form throw facility and command keys generating set sequence of signals from one key depression. 12 PRINTING REPERFORATOR REPRODUCER KEYBOARD TAPE PUNCH MODEL SEVENTY-FIVE PR TERMINAL SET MODEL 7P/N SERIES 2 A development of the basic Model The Creed Model Seventy-five The Creed Model 7P/N Series 2 Key­ Seventy-five Teleprinter, the Creed Reproducer/Terminal Set is a com­ board Tape Punch is widely used in Printing Reperforator is designed for posite, multi-purpose equipment, the communications and data proces­ the automatic recording of telegraph comprising: sing fields as the basic machine for messages and other data, both as 1. Model Seventy-five Teleprinter with transcribing source data into 5-track coded perforations and corresponding tape punch; punched paper tape. printed characters, on standard 2. Model 6S/6-M Tape Reader (auto­ Moderate cost, small-size, rugged 5-track +tin. (17.5 mm) wide paper tape. transmitter); construction and high speed of opera­ Like the parent Model Seventy-five tion are features which have contri­ 3. Equipped Desk with built-in push­ Teleprinter from which it is derived, buted to its appeal. button control unit. and with which it shares a high The machine is designed to cater for percentage of common components, Designed to meet a wide variety of the expanded codes that are finding this machine is outstandingly smaller application needs in both data proces­ increasing application in data proces­ sing and communications, the and lighter than the equipment it is sing systems, and three distinct designed to replace, whilst having the Reproducer/Terminal Set is outstand­ versions are available. ability to operate reliably at speeds up ing for its versatility of operation. 1. a narrow-tape version which to 100 w.p.m., with reduced Facilities for on- or off-line working, punches five code tracks in +tin. maintenance. page printing, tape editing, transmis­ sion and reception, all are provided (17.5 mm) wide paper tape; A feature of the Model Seventy-five within this compact, high-performance 2. a medium-tape version which Printing Reperforator is the position­ set designed to operate at speeds up punches six or seven tracks in ~in. ing of the printing between the to 100 words per minute. (22.2 mm) wide paper tape; punched sprocket-feed holes on the tape. With this arrangement a legible The Reproducer/Terminal Set is 3. a wide-tape version which punches printed record is obtained on fully available in two versions. These are eight code tracks in 1 in. (25.4 mm) wide punched tape of standard width virtually identical in appearance but paper tape. which may be handled by photoelectric differ in technical detail according to Also introduced is a new all-metal readers as well as conventional tele­ application needs. The Reproducer overall machine cover for improved graph transmitters. Printing on the version is designed specifically for appearance and utility. The punching tape occurs Bt feed hole pitches off-line tape editing operations in data mechanism is now fully enclosed for behind the corresponding code processing systems, whilst the protection against damage or dust perforations. If desired, a second tape Terminal Set functions as a complete while remaining instantly accessible may be punched (but not printed) telegraph station for the interchange via a hinged cover section incorporat­ simultaneously with the punching and of messages and other data over ing a window for viewing the punching printing of the original. communications circuits. If desired, operations. the off-line facilities of the Reproducer The Model Seventy-five Printing The tape supply reel is relocated in a can be combined with the on-line Reperforator is designed primarily for space-saving under-base drawer and signal transmission and reception on-line reception of telegraph signals, a larger copy holder provides greater facilities of the Terminal Set to pro­ but is available optionally with either a convenience for operators encoding vide a single multi-function station 3- or 4-row keyboard for direct on-line lengthy data such as computer offering exceptional versatility of manual signal transmission or off-line programming instructions. operation. A 5-wire Reproducer Set origination of code punched and which has parallel input-output is also printed tape. available. Where application needs do not demand a printed record on the tape, the machine may be supplied without its printing component for service as a simple 5-track, non-printing tape punch, operating at speeds up to 100 w.p.m.

13

GLOSSARY OF TERMS End-of-Line Indicator A mechanism attached automatically, the tongue moving over to the to the transmitter of a Uleprinter, to provide a send contact before the transmission of each visual or aural indication when a specific character signal. The return to the receive Abbreviation : ( BS) = British Standard number of keys have been depressed after the contact may take place either directly after the Carriage Return key. This device is used as a transmission of the character signal, or be Answer-Back A device which, when released warning to depress the Carriage Return key in delayed. by the receiving mechanism in response to an cases where there is no local record or only a Simplex System A telegraph system in appropriate signal from the distant end, con­ tape record at the transmitting end and the which the circuit is arranged for operation in trols the transmitter and causes it to send back receiving machine is a page machine. automatically the identity of the called station. one direction at one time (BS). Figure Shift One of the shifts into which the This facility assures the calling operator: Slip Term used to describe punched tape. characters and functions of the five-unit code (1) that he is connected to the station desired, are grouped. Space One of the two kinds of elements in the (2) that the called teleprinter is operating, even Five-Unit Code The CCITT No. 2 Telegraph international binary start-stop code, e.g. the if it is unattended, and code. last three elements of the combination for' A' in (3) if operated at the end of a message, that the Function A teleprinter operation other than the code are spClces. whole message has been received. printing or perforating which requires the Start Space Usually positive battery or no-cur­ transmission of a particular code combination Back Space Key A control fitted to keyboard rent signal which precedes every five-unit code perforators and reperforating attachments to (e.g. Line Feed). combination. This signal releases the receive­ feed punched tape backwards-usually so that 'Here-Is' Key Control for operation of local cam in the local and distant teleprinters to mistyped character can be erased by over­ 'Answer-Back Unit' to transmit identifying code ensure that both machines are in synchronism. punching the all-mark (letters) combination. name to distant station. Stop Mark Usually negative battery signal Keyboard Perforator Machine which pro­ which arrests the receive-cam of local and Baud The unit of telegraph speed. Telegraph duces punched paper tape (without printed distant teleprinter which then remain signals are characterised by intervals of time interpretation) from keyboard operation. stationary to await the start space of the next of duration equal to or greater than the shortest Letter Shift One of the shifts into which the character code. or elementary interval. Telegraph speed is, characters and functions of the five-unit code therefore, expressed as the inverse of the value Tape Low Alarm A visual alarm system fitted are grouped. of the elementary interval in seconds. A speed to many punched-tape machines to give warn­ of one elementary interval per second is Local Record A printed copy at transmitting ing that the supply of unpunched tape is termed one baud (BS). station of message sent to line manually or running low. automatically. The elementary interval for teleprinter trans­ Tape Read er Also known as automatic trans­ Margin The maximum distortion which, when mission is 20 milliseconds i.e. 1/50th of a mitter, this machine is designed to translate occurring on any or all of the signals applied to second. Therefore, the telegraph speed is 50 the coded perforations in punched paper tape a telegraph receiver, is compatible with correct bauds (see Telegraph Speed). into electrical signals at a steady, fixed speed. registration of all the symbols for which the Cadence Speed For teleprinters this is the receiver is designed (BS). Telegraph Distortion In telegraph systems in telegraph speed in words per minute. Two Mark One of the two kinds of elements in the which the signals at their origin are charac­ teleprinters having the same telegraph baud international binary start-stop code, e.g. the terised by modulation at specific instants, the speed do not necessarily have the same first two elements in the combination for 'A' in degree of distortion of the modulations when cadence speed: the code are marks. reproduced at the receiver is the ratio of the For a telegraph baud speed of 50 bauds, using Off-line Term used to indicate that a tele­ difference in delay or reproduction of the 7-unit transmission, the cadence speed is 71.4 printer or set of equipment is not connected to instants to the duration of the shortest modula­ words per minute. a signalling circuit or line. tion interval applicable to the particular system under consideration (BS). For a baud speed of 50 bauds, using 7!- unit Ori entation Device An integral unit in most transmission, the cadence speed is 66.6 words teleprinters to adjust the machine's operation Telegraph Speed The rate of transmission, per minute. so that the least distorted portion of each either in characters or words per minute, or in Case In telegraphy this term is often used incoming unit (or baud) signal is sampled and bauds. For the purpose of calculation, a word is synonymously with shift. fed to the decoding unit. This adjustment accepted as consisting of 5 letters and a space, ensures that slight line distortion does not or 6 characters (BS). CCITT No. 2 Code The internationally agreed result in mis-selections. 5-unit telegraph code. Telex The public teleprinter service operated Parallel Working Mode of operation where by the GPO and Post & Telegraph authorities Character A printed symbol. Characters may input and output is on a multi-wire simultane­ in most countries of the world. be letters, figures, punctuation marks or signs. ous basis, e.g. where signals are applied to five Signs may be sub-divided into operation signs or more lines simultaneously. Torn Tape Relay A system of message rout­ (e.g. +.f.=), abbreviation signs (e.g. @.£), and Reperforator An instrument which converts ing based on the removal of a punched tape functional signs (e.g. co= for Line Feed). incoming electrical impulses of the five-unit from a reperforator at a communications centre and feeding into an automatic transmitter Combination A particular arrangement of code into equivalent perforations of a paper connected to another circuit. This system code elements. tape. Run-out Key Operation of this control, which makes possible considerable operating econo­ Double-Current System A telegraph system is fitted to certain teleprinters and reperforators mies since it is necessary for every station in a in which signals are transmitted by reversing a causes the high speed repetition of the charac­ network to be connected only to the communi­ current that is normally on the line during ter associated with any other key held down at cations centre and not to all other stations. transmission (BS). the same time. 'Who Are You' Sig nal The code which when Duplex System A multiple-way system in Send-Receive Switch A switch used in transmitted to a distant teleprinter causes the which the circuit is arranged for simultaneous simplex systems for changing over from the answer-back unit to automatically transmit operation in opposite directions, over a single sending to the receiving condition, and vice back a station identification word or phrase circuit (BS). versa. On the teleprinter this switch is operated usually known as the Answer-Back Code. 16 • ••••• , • GOQQCD Creed & Company Limited · Hollingbury · Brighton · England · Telephone: Brighton 507111 ·Telex 87169

© 1966 by Creed & Company Limited Creed policy is one of continuous improvement and the right is reserved to revise equipment specifications and details published without prior notice

CREED PUBLICATION 041--Q30-1E Printed in England