kdr wrote on 2022-09-22, 09:42:

vstrakh wrote on 2022-09-22, 08:58:

There are clear signs of bus contention visible on the oscilloscope waveforms.

Not necessarily. While CMOS drives 5V for a logic '1', the 74xx series TTL has weak logic '1' levels and can only get the output up to 3.6V-3.8V or so.

It's possible, but those short spikes up and down - those are too short and too fast rising to be explained just by pullups and the periods when no IC is driving the bus.
Yet it fits perfectly the case with multiple drivers with signals shifted in phase.

weedeewee wrote on 2022-09-19, 14:57:

Any chance you can dump & upload the bios ?

My TL866 just arrived and I dumped the BIOS.

https://s3.us-west-2.amazonaws.com/jason.sper … /2764-DIP28.bin

The chip is a Mitsubushi M5L2764K, while the Programmer doesn't support the 21v needed to write to this chip it does support the 5V required to read it, and after checking out the datasheet it appears the chip is interchangeable with Intel 2764 which if I select and remove the "Check ID" reads just fine. Looking at the hex viewer the bios reports that it's for "Compatible Computer TURBO BIOS For PC, XT-16" and at the end of the ROM is the date: 10/16/1984. Now to find a compatible EEPROM that I can write with this programmer.

Unfortunately another dead end. I programmed an M27C256 with Rudd's Diagnosis BIOS but when I try to boot up the computer I'm still not getting any POST codes on the PC analyzer, no beeps on the speaker and no output from the CGA card. One other thing that might be an issue, I had plugged in a keyboard that I know works into it and later when I put that keyboard back into a 386 that I have the keyboard no longer seems to work. I get a flash of the LEDs and the 386 isn't reporting a missing Keyboard error but the keys no longer seem to send any information to the computer. I haven't dug into any of the output voltages from the keyboard port on the 8088.