I confirmed that the CTRL and BREAK keys have continuity up to M25 and M15.
With power removed from the unit, I have normal DMM readings at each chip when
the keys are depressed (diode mode).
When looking at ROM pin 20 (A11) with an oscilloscope, no waveform is present,
only 5V with a bit of noise. M3/M4 Pin 1 (A11) and M21 Pin 14 (A11) looks
similar however there is a small difference in the noise level around the 5V.
Thank you for providing the code for the test harness. I'm still learning but
I'll see if I can follow along! Let me know if you have any other tips for
troubleshooting this issue.
Eric
On Wednesday, January 3, 2024 at 01:09:38 PM PST, <[email protected]>
wrote:
Is it possible that your CTRL or BREAK key are not working, thus you are not
able to do a cold reset? It could also be the M2 data bus latch has the bit you
mentioned stuck. Sometimes you can look at a suspect bit on the oscilloscope
and see incorrect voltage levels, or what looks like multiple signals at once.
Note that with the multiplexed bus this can be difficult to spot as there are
some ‘normal’ goofy looking waveforms when the bus is being multiplexed.
The code for the test harness test ROM is here:
https://github.com/Jeff-Birt/TRS-80-M100-M102-Test-Harness . The test harness
ROM board has a small built in LCD for feedback. You won’t have this but you
can follow how far it gets though the test with your LA.
Jeff Birt
From: M100 <[email protected]> On Behalf Of Eric
Sent: Wednesday, January 3, 2024 10:23 AM
To: [email protected]
Subject: Re: [M100] Model 100 - LCD Shows Pixels Only
Yes, I did hold down CTRL+BREAK+press reset. Repeated this three times and the
data is almost identical (repeatable results). I triggered off of the reset
signal and recorded 100ms pre-trigger and 2s post-trigger. Performed data
review just after the RESET occurred.
Thanks again for everyone's help with this. I'm learning a lot about this
computer and feedback from the forum has been very inspiring!
On Wednesday, January 3, 2024 at 05:12:15 AM PST, <[email protected]>
wrote:
