Guys —
I finished my
MiniFP board this morning and I can’t seem to deposit
to or read from memory using the EXAMINE toggle. The
“next” part of the function works, so I can step among
addresses but the data LEDs are all on all the time
(unless I set JP5 SSW_DSBL jumper). However, if I use
the SINGLE_STEP switch, the data bus LEDs appear to
reflect memory contents.
The experimental
system is very simple CompuPro RAM17 (64k), IMSAI 8080
board, and the front panel. Before I say that anything
is wrong, can someone confirm the jumpers? I think
only the MWRT should be jumpered. The RAM17 is an
IEEE-696 board so as I do for my IMSAI, I’ve isolated
pins 20/70 (UNPROT/PROT) on that board.
Chip-wise, I’ve
used LS (including the LS123 as recommended in the
Wiki) except the 7402. I don’t have any 7400’s
in-stock so I’m using LS00 for now…don’t know if
that’s part of the issue since those gates are used in
the EXAMINE circuit. I replaced the 8212 just in case,
but that had no effect. The data cable is fine.
Any help, even
questions to get me thinking, would be appreciated. I
feel I’m pretty close to a solution here.
Thanks!
Rich
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Rich Cini
Collector of Classic Computers
Build Master and lead engineer, Altair32 Emulator