4 Sep
2014
4 Sep
'14
11:57 a.m.
Let's see... the address lines for the A20A2 PROMs
are labeled "CONF ROM
ADRS 00 (1) H" and the address lines for the A11A2 are... "CONF ROM ADRS
00 (1) *L*." So my A11A2's contents are backwards because the address
lines for that PROM are active low. Why? Good question. To make my
life miserable, I suppose.
My guess (without checking the printset) is that the microcode program
counter register has both Q and Q/ available. By using both (some ROMs on
Q, some on Q/ ) you can meet the fanout requirements, there may be too
many ROMs for the address pins of all of them to be driven by a single
set of TTL outputs.
At least they didn't feed soem ROMS with a mixture of Q and Q/ signals --
did they???
-tony