Synchronous serial Re: E-Mail Formats RE: Future of cctalk/cctech

Paul Koning paulkoning at
Fri Jun 19 12:43:04 CDT 2020

> On Jun 19, 2020, at 10:43 AM, Ethan Dicks via cctalk <cctalk at> wrote:
> On Fri, Jun 19, 2020 at 4:26 AM Dave Wade via cctalk
> <cctalk at> wrote:
>> Its been ages since I did this but looking here
>> 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.


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