30 Apr
2015
30 Apr
'15
9:31 p.m.
Hm.. I could have sworn they were the same. Oh well.
Figures. :-)
It's been many years since I looked at the printsets, but I thought the M9301
had 4 off 4-bit wide PROMs that were read out together to make a 16 bit
word, and that therefore all 4 PROMs have to be present. The M9312 uses
hardware to read a 16 bit word out of 4 locations in a single 4 bit wide PROM,
so the 4 PROMs on that card are independant of each other, each normally
contains the bootstrap for a particular device.
-tony
The M9301 has four 4b wide proms configured as a
512x16 and the console
and device boot code all live in this address space.
That is also true of the M9301.
The M9312 (and the 11/44 also) have one 4b
console PROM, and four slots
for 4b wide device boot PROMs. Each of the PROMs are nibble accessed to
build a 16b word from four 4b nibbles. The PROMs are all independent of
one another.
Yes. And this is more or less also how it works on the M9301. However,
it seems that DEC didn't actually put difference devices in their own
roms for the M9301, but treated the whole ROM memory as a big chunk with
a bunch of different devices bootstraps in there.