exxos's Atari, Amiga & retro forum

Kepler wrote: 12 Jun 2024 21:43 With the _HLT pin raised, the pin registers low and the socket registers high. Therefore, it appears it is the CPU which is causing the halt. Correct?

Yes there has been a bus error. I dont have schematics for the A2000 handy but i'm thinking it could be a bus buffer pulling the data bus bad. if you buzz out data bus between the rom and the CPU and find no shorts to ground, vcc and no breaks then it could be that

By "bus buffers", do you mean U604 and U603?

Kepler wrote: 12 Jun 2024 22:38 By "bus buffers", do you mean U604 and U603? Screenshot_20240612-223655~2.png

Yes. Those ones. Check pins 1 and 19 wiggle?

Annoyingly i could find this in a couple of minutes with the logic analyser.

By "wiggle", I assume you mean fluctuate high and low?
I have just checked and both 1 and 19 on both ICs remain high.

Kepler wrote: 13 Jun 2024 07:06 By "wiggle", I assume you mean fluctuate high and low?
I have just checked and both 1 and 19 on both ICs remain high.

That means it doesnt even get as far as talking to the chipset... try pulling the CIAs out and see if DiagROM gets any further?

Unfortunately, no further with both CIAs removed.

Perhaps we are approaching this from the wrong direction...Would it not be possible to start the debugging process from the first power on?

The power supply is switched on and the board is powered, does anybody know what is supposed to happen next in relation to component initialization and execution? I know that may seem a bit vague but I feel it is the only way I will fix this.

Kepler wrote: 14 Jun 2024 10:27 Perhaps we are approaching this from the wrong direction...Would it not be possible to start the debugging process from the first power on?

The power supply is switched on and the board is powered, does anybody know what is supposed to happen next in relation to component initialization and execution? I know that may seem a bit vague but I feel it is the only way I will fix this.

DiagROM will read from ROM and immediately print to the serial port (via paula). If you arent seeing anything on the serial port then it cant even execute the first handful of instructions which implies databus/address bus issues.

DiagROM will work with a very broken system. It will run with no ram in the machine, Denise missing and a broken Agnus. It really only needs Gary to be able to decode ROM.

Perhaps check the ROM OE pin is low at boot?

Thanks.
ROM OE is high at power on with Diagrom.

It shouldn't matter which ROM you have in the machine for the /OE signal as that's an input to the ROM to tell it to output data onto the bus.

The Amiga 2000's ROM socket is wired up to accept the type of ROM chip that DiagROM is written into isn't it? Something to check as at least some of the A500s have different pin outs and the 2000 is based upon the same design.