daver2
10k Member
Agree, please check again.
EDIT: But the CPU is executing instructions - yes (SYNC pin of CPU oscillating)?
The state you imply is that the CPU is executing code in RAM between $0000 and $0FFF - implying that the CPU is not obeying the instructions from ROM.
No, it doesn’t imply that the CPU is faulty either!
More likely there is an issue with the ROM, it’s address decoding (/CS line from UD2 pin 17 to UD9 pin 20) or the data bus is becoming corrupt.
What we need to do next (after checking for continuity from UD2/17 to UD9/20) is to look for signs of activity on UD9/20 just after a reset condition.
For that, we need to use our trusty scope...
But do the above first.
Dave
EDIT: But the CPU is executing instructions - yes (SYNC pin of CPU oscillating)?
The state you imply is that the CPU is executing code in RAM between $0000 and $0FFF - implying that the CPU is not obeying the instructions from ROM.
No, it doesn’t imply that the CPU is faulty either!
More likely there is an issue with the ROM, it’s address decoding (/CS line from UD2 pin 17 to UD9 pin 20) or the data bus is becoming corrupt.
What we need to do next (after checking for continuity from UD2/17 to UD9/20) is to look for signs of activity on UD9/20 just after a reset condition.
For that, we need to use our trusty scope...
But do the above first.
Dave