Fiddling with MSI88/e

 

Hello all,

I've been playing with the MSI88/e this weekend, using Lee Hart's
partial reverse-engineered schematics from the FILES section.

Looking at these, it seems that EF3 and Q are wired to the port in a
way that could support a bit-banged serial interface. It so happens
that Lee has also written the code for that in his IDIOT/4 monitor,
which comes complete with TMSI tiny BASIC.

I assembled the TMSI BASIC source, configured for 8K ROM (PAGE=2000H),
with SEQ/REQ reversed (to account for the inverted buffering of Q),
and using EF3 instead of EF4. The goal is to explore the unit
interactively via a terminal. I can see valid serial data from the
remote terminal on pin 22 (EF3), but no activity on Q. I did remember
to fill the unused ROM with FF to keep the startup code from trying to
execute a ROMed basic routine. I

To try to isolate the problem, I also tried a little program:

0000 36 05 LOOP B3 QOFF
0002 7a REQ
0003 30 00 BR LOOP
0005 7b QOFF SEQ
0006 30 00 BR LOOP

(At my programmer, I couldn't remember the code for SKP)

Again, no terminal echo, and no activity on Q, despite clock at pin 1
and valid logic signalling at EF3.

Interestingly, I notice that after powerup, the clock doesn't seem to
start up until the right-hand switch on the display board is toggled.
Forcing a reset by pulling pin 3 (CLR) low has no real effect.

It sure would be nifty to get one of these little buggers up and
running :-) Anybody have any insights, corrections, or suggestions?

Thanks,

Dave

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