A switchboard between the computer and the teletype printer

T. A. E. C.

ÇEKMECE NUCLEAR RESEARCH AND TRAINING CENTER İ S T A N B U L - T U R K E Y

ÇNAEM-R- 179

A SWITCHBOARD BETWEEN THE COMPUTER AND THE TELETYPE PRINTER

Toygun S.BAŞOL

P .K . 1y Hava Alanı, Istanbul, Turkey

T. A. E. C.

ÇEKMECE NUCLEAR RESEARCH AND TRAINING CENTER İ S T A N B U L - T U R K E Y

ÇNAEM-R- 179

A SWITCHBOARD BETWEEN THE COMPUTER AND THE TELETYPE PRINTER

Toygun S.BAŞOL

P .K . 1, Hava Alanı, Istanbul, Turfcey

ACKNOWLEDGEMENTS

I am indebted to Professor Arne Johansson for providing

good experimental conditions at the Uppsala Tandem Accelerator Laboratory. The author is indebted to the electronic workshop for help with the construction of the prototype of the switch­ board.

ABSTRACT

In order to make the communications with the OLDA on-line program at Tandem Accelerator Laboratory, faster and more conve­ nient a switchboard was constructed. The switchboard is supposed to be connected between the computer and the on-line teletype printer (TTY). It is an alternative source of some of the more xrequent commands to the OLDA program with a complete command in one key instead of the normal 4-key commands ( 3 character command + carriage return ) used with the TTY. Besides, when you use the switchboard, you don't have to wait for the time-consuming TTY-printouts before you can give another command.

Ö Z E T

YAZICI VE BİLGİSAYAR ARASINDA BİR " SWITCHBOARD "

Tandem Akselerator Laboratuarındaki OLDA on-line programı ile iletişim kurmak için mevcuda göre daha hızlı ve daha elveriş­ li olan bir Switchboard'un tasarımı ve imali gerçekleştirildi. Switchboard, bilgisayar ile on-line uzak yazıcı (TTY) arasında yer alacak biçimde düşünülür. TTY kullanıldığında olağan 4 tuşla elde edilen komutlar, OLDA programında çok sık olan komutlardan bazıları için bir seçenek kaynak olan switchboard'da tek bir tu­ şun basılması ile sağlanır. Bundan başka, Switchboard'u kullana­ rak TTY nin "dışarıya basması" ile oluşan zaman kaybını beklemek­ sizin diğer bir komut gönderilir.

C O N T E N T S

1. INTRODUCTION 1

2. GENERAL DESCRIPTION OP THE SWITCHBOARD 2

2.1 SHIFT REGISTER UNIT 2

2.2 CLOCK UNIT 3

2.3 KEYBOARD UNIT 3

2.4 CONTROL UNIT 3

3. CONCLUSION 4

A SWITCHBOAED BETWEEN THE COMPUTER AND THE TELETYPE PRINTER

Toygun S. Başol 1

I - INTRODUCTION

In a modern nuclear physics laboratory, there are many

possibilities to provide communication with the on-line computer* One of them is the teletype (TTY) printer unit, another is the computer display terminal. Paper tape, magnetic tape unit, disks, punched cards, magnetic tape cassettes etc., are other input-output units of the computer. (1,2)

By means of the TTY, the data can be sent to the computer

character by character (3,4) and receiving the echo signal from the computer is possible, too. The character is composed of ASCII bits, start bit and stop bits. There are two types of characters such as alpha-numeric characters and control charac­ ters. One can generally use on the keyboard of the TTY one key for each alpha-numeric character and specially two or more keys for control characters.

In order to make the communication with the OLDA (5) on-line program at Tandem Laboratory in Uppsala faster and more

convenient a switchboard was constructed. It is supposed to be connected between the computer and on-line TTY printer.

By means of this switchboard ASCII characters between the octal codes 040-057 and 140-157 c°n be sent to the computer. In this switchboard, to be able to use only one key instead of two or more keys is provided in a narrow region of ASCII character field. Namely, it is time gaining from the point of the user. An other advantage of this switchboard one can be able to use the ASCII characters up to the 140-157 that TTY is not proyided with this facility.

Following is explained the operation of the device.

Depressing a key on the keyboard each II bits of the characters c»n be sent to the computer at two separate phases and can be waited for their echos in a short time duration. Naturally, reaching the TTY echos of each II bits of the characters sent from the computer is prohibited. Every phase can contain each II bits of the characters and their echo bits. In order to be able to complete the phases, switchboard can generate the necessary signals by itself, if the computer can't send the echo bits. Therefore the switchboard is always ready to serve the user. Of course when the switchboard is operated, using of the TTY is prohibited.

2 - GENERAL DESCRIPTION OF THE SWITCHBOARD

The switchboard consists of four separate units called shift register, clock, keyboard and control. In a block diagram, uni+s, relations between the units and the external devices are shown in figure 1. Circuit diagram of the switchboard is also shown in figure 2. While constructing the whole device, the TTL family IC's

and passive standart circuit elements has been used.

2.1 - SHIFT REGISTER UNIT

Data at 22 parallel access inputs of the circuit is serially conver­ ted to the output at the two separate phases (6).5 of 22 bits at the

parallel access inputs are provided by the keyboard and other

input bits are provided by the shift register. Changable and unchangable logic levels at the parallel access inputs of shift register are like as below so that when they are leaving in order from the serial output in two separate phases:

(H,X,X,X,X,L,H,X,H,L,L); (H,H,L,H,H,H,H,H,H,L,L). The phases de+ermined by the control unit and in each phase II bits of a char-cter is sent to the computer. In order to open the receiver way between the computer and the TTY for the communication, 1. and 13. inputs of the shift register are held at low level when the characters have not been sent.

3

-2.2 - CLOCK UNIT

The clock unit is utilized either during the sending time of the characters from the shift register to the computer or in order to load the different counters used for different purposes in the control unit. The operating frequency is adjusted to 110 Hz under the load, at 5 7 dc voltage and at the costant l«boratory

temperature. Constructing the clock unit (7), an integrated circuit called commercially 555 and passive circuit components are used. Connection diagram of the clock is taking place in the circuit diagram of the switchboard shown in figure 2.

2.3 - KEYBOARD UNIT

By means of this keyboard unit the whole manual commands can be given. This unit has 32 manual command keys. There are 6 outputs of the keyboard, 5 of them are directly connected to the parallel access inputs of the shift register. Whenever one depress a key on the keyboard, a strobe signal is obtained at the 6. output of the keyboard.

2.4 - CONTROL UNIT

By means of this unit the tasks explained below are achieved: a) The transmitter way between the computer and the TTY is controlled.

b) The data in the shift register is transferred to the computer at two phases being II bits of the characters.

c) The first bits of the echo characters sent by the computer are recognized.

d) If the computer can't send the echo characters, the neccessary signals instead of the first bits of the echo characters are

generated and the device is prepared by itself for a new operation. e) By means of the synchronization of the clock pulses, the first bits of each characters with a normal duration is sent to the computer.

4

By means of a strobe pulse, sent by the keyboard, following duties are achieved:

a) Data at the parallel access inputs of the shift register is entered

b) Data at the serial output of the shift register transferred to the computer with a starting pulse is generated at a special instant of each phase.

c) The counters are reseted

d) The programmable counters are seted to the presetable values e) The device is prevented from being paralyzed gven if the computer can't send the echos.

Pulses at different points of the control unit produced by the strobe pulse are shown in figure 3 and figure 4»

Signal levels of the current loop between the computer and the TTY and signal levels at the output of the switchboard adapted respectively by the control unit. Adaptation of the signal levels achieved with the opto-couplers are shown in figure 2.

In order to prevent the detection of the first bits of the echos by the TTY, there is a delay circuit on the receiver way between the computer and the TTY and necessary conditions are satisfied by the control unit.

Flip-flops, delay elements (8), varios gates, counters and passive circuit components are used in the control unit.

3 - CONCLUSION

The swithcboard has now been in succesful operation for over 1 year. It has proven to be a very flexible unit. The switchboard has a few advantages, on the contrary TTY is not provided with these facilities.

- ASCII octal codes up to the 140-157 can be used

- Some of the command characters can be transferred to the computer depressing only one single key on the keyboard.

REFERENCES

1. W.W. Black., An Introduction to On-line Computers, Gordon and Breach, Science Publishers, Inc, 1971.

2. J.D. Schoeffler, R,H. Temple., Minicomputers: Hardware Software and Applications.

3. G.A. Korn., Minicomputers for Engineers and Scientists McGraw Hill Book Company, 1973.

4. Instruction List for the PDP 15.

5. «J. Phil., The Tandem Accelerator Laboratory On-Line Data Acquisition System (Tmolda).

6. R.C. Pasco, Electronics, Oct 30, 1975, pp 97-98

7. F.N. Cicchiello, Electronics, May 13, 1976, pp 95-96 8. The TTL Application Handbook, Fairchild Semiconductor,

2

0

0

Tim ing d ia g ra m o f the s w itc h bo a rd .

STROBE PULSE

p o i n t(x)

74123 D P I N 13

1 s ■1 s ■

7 4 1 0 P I N 13

k

Fig. A_ Pulses generated at different points by the control unit when the computer can't send the echos.