[GreenKeys] Teletype 3320

[Chris Elmquist]

On Sunday (03/07/2010 at 12:50PM +0100), Nico de Jong wrote:
> Hello fellow greenkeyers
> 
> For the danish IT museum, I need to connect a Teletype ASR 3320 to a 
> comport, so we can simulate the old european Gentex network.
> This 3320 has probably been connected to a PDP mini or similar.
> There connecting cable uses 5 pins : 2, 3 and 7, which is straightforward, 
> plus 24 and 25.
> My questions are :
> - what could 24 and 25 have been used for

These are where the pins start to diverge from any RS232/EIA/V. standard.
People used them for all sorts of unique applications.

V.21 says that pin 24 is,
	Transmit Signal Element Timing (DTE Source)

and pin 25 is,
	Test Mode

but who knows??

Does the unit have a tape reader?  If I had to guess, I'd say someone may
have mod'd it so that they could start and stop the reader with signals
on those pins.  This was a common mod in the early mini and microcomputer
days with no real standard on how those signals were brought into and
out of the TTY.

> - is this a straight RS232 machine, or do I need a 20 mA current source

Pins 2, 3 and 7 sure suggest to me that it is straight RS232.

The TTY will transmit on pin 2, receive on pin 3 and 7 is ground.

You might try hooking the TTY to a PC using only pins 2, 3 and 7 and
then see if you can communicate with it using a terminal emulator, while
just leaving pins 24 and 25 open.

> All the best

Good luck!

Chris

-- 
Chris Elmquist