I've never seen an ALTAIR (beyond the Popular Science cover!) or used the
emulated simh version, but I was reading code for edification and came across
this statement in altair_cpu.c:
3. Non-existent memory. On the 8080, reads to non-existent memory
return 0377, and writes are ignored. In the simulator, the
largest possible memory is instantiated and initialized to zero.
Thus, only writes need be checked against actual memory size.
This looks like boilerplate copied from other simulators. Sure enough, later
on, I find:
for (i = MEMSIZE; i < MAXMEMSIZE; i++) M[i] = 0;
However, if the statement above regarding 8080 behavior is correct, and I have
no idea if it is, shouldn't that line be:
for (i = MEMSIZE; i < MAXMEMSIZE; i++) M[i] = 0377;
to preserve accuracy of the simulator?
FWIW,
Scott Bailey
scott.bai...@hp.com
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