Oh I misunderstood that. I thought the tnc had that configurable with a
jumper installed by default.
--
bkw
On 9/27/23 19:37, Jesse Bertier wrote:
I agree that the m100 has unique circuitry contributing to the problem -
perhaps only 5 volts to work with , perhaps the choice in the resistor values
chosen on the inputs and outputs, or perhaps when they changed to 330 ohm
values in that TSB.
Agreed it’s perfectly legit to loop back in this fashion. What’s odd is other
older TNCs didn’t do this, at least not by default. What I didn’t try yet is
seeing if tickling the DTR output on the m100 changes anything (switching it
from high to low or vice versa). That built in telcom program initializes the
uart and resets the hardware flow control lines, so I would need to write
something in basic to do the test.
Unfortunately that tnc has traces needing to be cut on the pcb to disable this
loop back. They didn’t put jumpers on the loop back options. Sacrificing one
of those gender changers was the lazy way to fix it.
Sent from my iPhone
On Sep 27, 2023, at 6:57 PM, Brian K. White <b.kenyo...@gmail.com> wrote:
On 9/27/23 16:01, Jesse Bertier 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.
It's still curious, because looping back those two lines is perfectly "legal".
It may possibly have a bad effect in some cases simply because of any signal
being a lie, but electrically it's perfectly legit. And it's not even a data
problem if neither side is looking at the signal.
I say, this indicates a problem in the 100 (in the design of the circuit, not a
damage you can repair) not a problem in the radio.
Though the work-around is still fine. I just mean that the conclusion that "aha, the
radio is the culprit" isn't really the case in my opinion. But even if I think the
root blame belongs to the 100, I'm not sure there is anything you can do practically to
fix the 100, and it was simple to make use of an optional configuration in the radio that
was put there basically just for this reason, to cater to the failings, or more
generously, quirks of other equipment that might need it.
--
bkw
If interested, I posted the details here:
https://n1ugk.com/2023/09/trs-80-model-100-with-the-kpc-3/
<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
--
bkw
--
bkw
