Fellow M100 Enthusiasts: I kept at it, trying all the various suggestions from the group. I finally solved the issue - the TNC had a loopback connection from DTR to DSR. The problem disappeared entirely when I removed that loopback connection the TNC was doing.
If interested, I posted the details here: https://n1ugk.com/2023/09/trs-80-model-100-with-the-kpc-3/ With that mystery solved, I can now use the M100 for what I intended to use it for. > On Sep 8, 2023, at 7:28 PM, Daryl Tester > <[email protected]> wrote: > > On 9/9/23 00:10, Jesse Bertier wrote: > >> I wanted to follow up with this issue - As it turns out, the TNC itself >> seems to be the culprit, at least with the M100. Even small text strings >> get garbled, with software flow control enabled on both sides. That TNC >> works fine with a PC, just not the M100. Next time I have the scope out, >> I’ll take a look at the line and compare, and work back into the M100 as >> needed out of curiosity. > > Sounds suspiciously like clocking tolerances (of the serial line). I thought > it used to be 20% (from the "olden days") with 16x oversampling), but current > Internet Wisdom (for what that's worth) says ~ 5%. If you've got one device > that's slightly fast, and the other slower, you''ll see this sort of > behaviour. > > (I used to work on a serial port switch in the 80's. That sod had something > like > a +0.5% tolerance, although its negative was relatively normal. The above > fault > was well known). > > Cheers, > --dt
