Re: [M100] Intermittent problem at higher baud rates on RS-232 interface

[Jesse Bertier]

Hi Alex, Yes, I’ve noticed the lcd dimming on the model 100 sometimes as there was higher current drain or voltage drain from the RS-232 port. I suspect hardware flow control lines is a big contributor to that power drain - anything that pushes the hardware flow control input pins high (I believe they’re pulled down to -5volts within the model 100).   I’m glad it’s now working - and I remember the MFJ model you mention, that was my first TNC . 73 Sent from my iPhone On Sep 27, 2023, at 6:28 PM, Alex ... <abortretryf...@gmail.com> wrote:  Jesse, I feel like I ran into that exact problem before a couple years ago when I was using my '102 for packet radio. Something also about poor battery life from the laptop while the TNC was plugged in as well? I didn't keep good notes, and I was testing several TNCs (two KPC-3s, a KPC-2, and a MFJ-1274. Thanks for documenting all the detailed measurements and sharing it with the group! -Alex On Wed, Sep 27, 2023 at 4:08 PM Jesse Bertier <berti...@gmail.com> wrote: 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 <dt-m...@handcraftedcomputers.com.au> 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 -- Disclaimer: Any resemblance between the above views and those of my employer, my terminal, or the view out my window are purely coincidental.  Any resemblance between the above and my own views is non-deterministic.  The question of the existence of views in the absence of anyone to hold them is left as an exercise for the reader. The question of the existence of the reader is left as an exercise for the second god coefficient.  (A discussion of non-orthogonal, non-integral polytheism is beyond the scope of this article.) Thanks /usr/games/fortune