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Using an ASR 33 Teletype with IBM PC


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  Using an ASR 33 Teletype with IBM PC by Bill Degnan - 06/14/2011 20:56
There is a socketed shunt module on the bottom right of the original IBM async board, just pull it out and re-insert upside down (so the dot is pointing down) for current loop. If you're going to use slot 8 of an IBM PC or XT a jumper is required on connector J13. Why I don't know off-hand.

Plug a regular-old EIA connector into the serial card in the back. The serial connector pins you need to connect to the teletype are are:

pin 9 = + transmit current loop data
pin 11 = - transmit current loop data

pin 18 = + receive current loop data
pin 25 = - receive current loop data

[pin 25 is the bottom right (bottom = row of 12 pins)]

Then connect to ASR 33:

Transmitted data return (-) attaches to terminal strip screw 6 or "number 2 connector" #7

Received data return (-) attaches to terminal strip screw 3 or num 2 connector #5

Transmitted data send (+): Terminal Strip 7, #2 connector 8

received data send (+): Term strip 4, #2 connector #6.

If the tty stops chattering you at least have a current loop. You'll need some sort of terminal program just like you'd use with an RS232 terminal connection, but you will need to use 110b, etc.

Source - Paraphrase from IBM Technical Reference Manual volume 2

  Using ASR 33 as IBM PC Console by Bill Degnan - 02/08/2013 09:51
If you have an IBM Asynchronous Communications Adapter configured for current loop, then you can in theory use a teletype as the console to interface with the PC.

MODE COM1:110,N,8,1

[I need to try this myself, if anyone reads this post and has corrections please advise.]


Using the software that came with the IBM Asynchronous Communications adapter it should also be possible to make a direct connection to the teletype via the serial port and use to upload ASCII into a file (while papertape is being read in by the TTY reader)

  Cable for IBM PC to Teletype by Bill Degnan - 02/11/2013 22:09
In addition to connecting pins 9,11,18,25 from the async card to the teletype, Chuck(G) of forums says "...the PC still pays attention to DSR, DTR, RTS and CTS. So you still have to jumper 4-5 and 6-8-20 on the PC DB25. ..

Request-to-send -> Clear-to-send (pin 4 to pin 5)
Data Set Ready -> Carrier detect -> Data terminal ready (pin 6 to 8 to 20)"

Thanks Chuck!

  IBM Async Card Current Loop Jumper by Bill Degnan - 02/19/2013 21:02
Photo of the jumper in the "current loop" position.



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