> On Jun 18, 2020, at 3:26 PM, Ethan Dicks via cctalk <cctalk@classiccmp.org>
> wrote:
>
> On Thu, Jun 18, 2020 at 3:08 PM Chuck Guzis via cctalk
> <cctalk@classiccmp.org> wrote:
>> On 6/18/20 11:55 AM, Ethan Dicks via cctalk wrote:
>>
>>> We used to run our sync serial stuff between 9600 and 56kbps, both our
>>> own Bisync products, and DDCMP over interfaces like the one that's
>>> part of the DMF32...
>>
>> My recollection of the Bell 209 is that it supported a low-speed reverse
>> channel in addition to the FDX primary.
>
> I had to look that up. Yes. I see that in the spec, at *5*bps.
Wow, that's weird.
>> Did any DEC equipment ever take advantage of that?
>
> I've never encountered it before, so I cannot confirm.
Not that I know of.
I did see something vaguely similar. Bell 202 modems are 1200 baud FSK, so on
a voice channel they normally are 1200 bps half duplex. They can also be
hooked up to 4-wire fixed circuits. But they have a reverse channel, good for
150 baud if I remember right. PLATO used that in its original terminal
connections, in a slightly strange way: 1260 bps data to the terminal, and 126
bps data from terminal to host. The protocols are peculiar: terminal output is
"synchronous", 21 bit frames at 60 frames per second, but each frame has a
start bit (no stop bit). Data to the host is asynchronous, 1 start, 1 stop
bit, 10 data bits. Since a 202 modem is just plain FSK, it doesn't matter that
the data rate is not quite the standard 1200 bps.
paul