Could use some help debugging my Omega cartridge slots

Supporter (12)

21-03-2023, 01:56

I have my Omega computer built, and have gone through many tests - everything seems to be working except for booting a cartridge.. Screen, sound, joystick, even tested cassette and it's working perfectly (loaded Donkey Kong from a wav file, what a blast!)

But when I put in a cartridge the system just boots to MSX-BASIC. Voltages look correct. I've double-checked my slot select/dir GALs, the CS lines all seem to be operating.

Does this timing look correct? This is a boot-up from power off, with a cart in Slot 1.

Let me know if there are any other lines that would be more helpful from a logic analyzer perspective.

By nullvalue

Supporter (12)

24-03-2023, 02:00

All I've found to go on is this page for the Cycle M1 timing. Can anyone point me in the right direction? Looking for something that might go into a little more detail...Such as how does the computer know there's a cartridge installed in the first place? what's it looking for before it decides to boot to BASIC, instead? thanks

By mcolom

Champion (316)

24-03-2023, 10:20

You have some info here: https://www.msx.org/wiki/Develop_a_program_in_cartridge_ROM
Basically the BIOS scans the slots to find the signature "AB" and then it jumps to the INIT address specified at the ROM's header.

By nullvalue

Supporter (12)

24-03-2023, 14:37

Thank you, this is helpful.

By nullvalue

Supporter (12)

25-03-2023, 21:25

I have resolved this. After extensive testing of all the address & data lines to the cart slot, I found there was no activity on my D1 and D5 lines. Followed the traces and found there was no connectivity between the cartridge port and the IC U25. It must be a couple of cracked traces, although I could not see any evidence of this. I ran a couple of bodge wires and I'm booting from cartridge now!