Teletype 43

dave.g4ugm at dave.g4ugm at
Tue May 23 01:07:57 CDT 2017

You probably need a null modem cable. As a test try linking 4+5 (rts/cts) and 6+8+20 (dsr/cd/dtr) on the tty plug/socket. (25 way pins)
Then when the terminal brings dtr up (data terminal ready) it also brings up dsr (data set ready) and cd (carrier detect) so it looks like the modem is connected.
Same way when it uses rts (request to send) it also enables cts (clear to send) so the modem has given permission to send data..


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Jim Brain
> via cctalk
> Sent: 23 May 2017 05:58
> To: Ethan Dicks <ethan.dicks at>; General Discussion: On-Topic and
> Off-Topic Posts <cctalk at>; Paul Koning
> <paulkoning at>
> Subject: Re: Teletype 43
> On 5/22/2017 8:41 PM, Ethan Dicks via cctalk wrote:
> >
> > Do you have a "traffic light"?  I find them invaluable for diagnosing
> > handshaking and TxD/RxD swaps.
> Yep.  constant low on TX.
> >
> > What worked was a serial port on a desktop.  The first try.
> It's entirely possible, but I put a scope on the TX line, and I see no activity at
> all with the unit in DATA or TERM READY mode.  The DATA LED blinks, so I
> think I need to signal the Model 43 that it is "connected".
> As has been suggested, I joined GreenKeys and asked if someone has a
> similar setup that works, so I can replicate.
> Worst case is that the driver board has issues, which at least will narrow
> down my search.
> Jim

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