I would suggest making sure that signals are present at the roms first, then the rams.
Seeing signals at the processor is great but you need to trace them through to the memories. Seems that the system is always accessing memory. Io/m is low. Which chip or chips? If you can find a reason why either a rom or ram is not reading or writing correctly that would explain the issue. Ie the system is stuck in a loop somehow. On Sunday, February 20, 2022, Gsvacances Free <[email protected]> wrote: > Thanks for the advices Steve ! > > I did as you said and found that at reset, D6 and D7 briefly toggle but > then stay high on the 80C85 (and thus on other ICs as well). > I’d rather say AD6 and AD7 as I checked right on the processor, before > these signals are latched. > > On the address bus, A11 stays low all the time and A14 & A15 stay high all > the time. > But if I push the reset switch, they briefly toggle too and stay low for > A11 and high for A14 & A15. > > All other address and data signals are toggling. > > Pin 10 is low and pin 11 is high so the CPU is not interrupted. > > CPU pins 4-5-6 are all low during and after pushing the reset switch. > > The CPU CLK pin 37 seems fine. > > /RESET and RESET also seem fine going respectively low and high when I > push the RESET switch and then go back to hign and low. > > > Any suggestions ? > > > *From:* Stephen Adolph > *Sent:* Sunday, February 20, 2022 6:07 PM > *To:* [email protected] > *Subject:* Re: [M100] Model 200 with LCD all black from power on > > I think you need to start confirming that your memory systems are working. > > For the ram modules and main rom, check at the pins > > All address lines can be observed to toggle > All data lines similarly toggle > Chip select lines toggle > > I've had 2 t200 with broken traces in the past. > > Ram is provided by that separate board which is connected via a cable. > Worth a close look. > > Good luck > Steve >
