Tony wrote:
Do you have a logic analyser? If so, then I would try
looking at the 8080
address bus. See what bit of the program it's executing, see if it does
the right things when you press the keys, etc.
I have, it's a Biomation K100-D. When I first set it up Sunday afternoon,
and turned the LA on, the screen moves vertically. So I had to get the LA
in good working order first! As I have the operator & service manual, the
location of the vertical freq. adjustment was quickly found. The screen is
now steady.
I connected the pod B, 8 data inputs to the ROM address lines A0-A7, and
gave it a manual trigger to capture all it sees. At first I got too much
detail (address repeats several times), but after setting the clock of the
LA to sample at 10 ?s I got almost always consecutive addresses.
That depends on the length of the instruction. Anyway, I see the addresses
60-110 (octal) in the correct order and see the address jump at 101 to the
address 335 (a subroutine). I see the complete execution of the subroutine
and the return. Indeed going to address 105. That means the stackpointer
and the memory must be OK! ReturnPC stored in RAM, and retrieved correctly.
However, I can not check everything. Need to connect pod A, and have 8 more
data input lines to measure interesting things. And trigger facilities!
It's time to read the user manual of the LA, to do advanced measurements.
I still haven't got a clue what's going wrong ...
- Henk.
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