EIA/RAM-Combo board RAM upgrade

[Bob Hoffman]

In article <6536 at cup.portal.com> thad at cup.portal.com writes:
>Has anyone with a 2MB (motherboard) 3B1 been able to increase their system's
>RAM to 4MB using only the EIA/RAM-Combo boards?

The RAM memory map of the 7300/3b1 looks like this:

000000 - 1FFFFF		Motherboard memory (2MB)
200000 - 27FFFF		1st 512kb expansion
280000 - 2FFFFF		2nd 512kb expansion
300000 - 37FFFF		3rd 512kb expansion
380000 - 3FFFFF		4th 512kb expansion  (avail. only on 2MB board)

The 1.5MB on the EIA/RAM combo card sits between 200000 and 37FFFF.
I don't believe there are any jumpers to set the starting address of
the board, so you would have to hack the addressing logic to put the
board at 380000.

Maybe someone with schematics for the EIA/RAM card can enlighten
further.

	---Bob.

-- 
Bob Hoffman, N3CVL       {allegra, bellcore, cadre, idis, psuvax1}!pitt!hoffman
Pitt Computer Science    hoffman at vax.cs.pittsburgh.edu