> On Jun 19, 2020, at 10:43 AM, Ethan Dicks via cctalk <cctalk@classiccmp.org>
> wrote:
>
> On Fri, Jun 19, 2020 at 4:26 AM Dave Wade via cctalk
> <cctalk@classiccmp.org> wrote:
>> Its been ages since I did this but looking here
>>
>> https://www.aggsoft.com/rs232-pinout-cable/RS232.htm
>>
>> I see we have a transmit clock output on pin 24, transmit clock input on 15
>> and RX clock input on 17.
>> So if on checking with a scope I have clocks on 24, I would try linking 24
>> and 15 on one side to 17 on the other side.
>> If you have only one clock running then that goes to 15 and 17 on both
>> ends....
>
> None of the devices I worked with in the 80s and 90s had clock
> available on pin 24. I'm not saying none exist, but they weren't
> around in the era I was doing this.
I had the same reaction. The sync serial devices I know use modem-supplied
clocks. That's why there is such a device as a "modem eliminator", which is
different from the familiar asynchronous "null modem". A modem eliminator is
essentially a null modem plus a clock source along the lines discussed a day or
two ago.
If you had a sync device that had the ability to send a local clock out, you
could make a sync null modem that would just be wires, as an async null modem
is. Perhaps this is something RS232 standardized but that wasn't adopted in
the real world.
paul
