DEC Pro 350/380 Memory Cards - Interchangeability?

Paul Koning paulkoning at
Fri Sep 2 14:26:30 CDT 2016

> On Sep 2, 2016, at 3:05 PM, Ethan Dicks <ethan.dicks at> wrote:
> On Fri, Sep 2, 2016 at 2:44 PM, Paul Koning <paulkoning at> wrote:
>> Incidentally, the Pro technical manual says that the daughterboard can be up to 2 MB (but DEC only offers 512 kB).  It doesn't say how that is done.  It looks like the answer is that there are four RAS signals, so you can have four banks, 256k by 16 each.
> Hmm... 2 Daughterboards at 2MB each?  A full 22-bit boat of RAM?
> Sweet!  

I was talking about the Pro 380, which has only one daughterboard.  Still, 2.5 MB is not shabby.  See page 6-25 in the technical manual.

Then again: see also page 6-52 and 6-53, the memory config register.  And the description on page 26 of the Pro 380 schematics.  It says pretty clearly that you could use 256k DRAM on the motherboard, which (if you install all four banks) would mean 2 MB on the motherboard.   Both motherboard and daughterboard have two wires to indicate bank count (1..4) and a "256 kB memory chips" signal as well, so both are in principle capable of being up to 2 MB each.  What happens if you install 4 MB is not entirely clear, since the I/O page still has to go to I/O of course.

A four bank "256k" daughtercard would be straightforward; I figure you could do it with a few gates plus a 1Mx16 memory chip -- give or take the EDO issue discussed earlier.  Installing 256k memories in the motherboard of course is more of a job because you have to take the existing baord apart.

The Pro 350 only has one RAS signal.  Then again, the connector pinout (page 5-129) shows a "Bank" signal; I wonder what that means.  Does anyone have Pro 350 schematics?


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