6 Feb
2007
6 Feb
'07
3:37 p.m.
Now, I seem to
remember that on 80 column PETs, the 2K video memory is
made up of 4 1K*4 chips and that alternate characters are stored in each
pair of chips (one pair of chips stores all the chracters in odd-numbered
locations on the screen the other pair the characters in even-numbered
locations). That would explain why you have problems with alternate
characters.
Hmm... I didn't know about the even-odd interleave, but that'd be easy
to check against the schematics. And you guessed it,. Those RAMs are 2114s, a chip
well-known around here
for failing in oadd ways.
Exactly. In a PET, it's much more likely that a 2114 has failed than
a bus buffer or similar IC.