Problem with DEC LSI11 / KD11-F

Pete Turnbull pete at
Sat Nov 29 19:40:00 CST 2014

On 29/11/2014 23:03, Mattis Lind wrote:

> Further searching and I found the LSI-11 Systems Service Manual from
> August 81. It describes the various revisons of the M7264 and M7270.
> Originally the chip used -5.1 V Vbb. But M7270 and rev E an onwards
> of the M7264 use a -3.9 V Vbb, which implicated use of other chips.
> So, they are not compatble as it appears unless I modify the Vbb
> generation circuit on the board.

Does the Service Manual say anything specific about the ROM 
compatibility?  I wonder how important it is to match the ROM set to the 
Vbb value, and to what extent the change was for improved noise immunity 
or longevity.

They're clearly slightly different types of ROMs, though.  If you write 
the numbers in the standard way they'd be shown in, say, a DEC parts 
list, you can tell something about them.  For example, 23088A501 would 
be 23-088A5-01.  23- means it's a ROM (or at least a ROM-like 
programmable part; 21- is a microprocessor or copro); the next three 
characters are numeric digits specifying the ROM number; "A5" tells you 
about the width and technology (the 'A') and the size in kilobits.  So 
B5 and A5 are presumably slightly different technologies - but as the 
socket layouts are the same, presumably the same width.  Incidentally, I 
don't know what Bx means but every Ax I've seen is a bipolar PROM.

The -01 is like a version number (sometimes used for different suppliers 
of the same device in other types of parts).  I've never seen anything 
other than -01 for a ((E)P)ROM, though, because DEC seem to have always 
changed the 3-digit code for even the most trivial changes to content. 
Note there's no relationship between numbers for successive revisions. 
For example 23-264E4/23-265E4 and 23-188E5/23-189E5 are both RQDX2 ROM 
sets but the lower-numbered one is the later version (V.10.0E; the other 
is V8.0).

BUT, as an aside, they did occasionally reuse triplets, requiring you to 
read the next two characters as well.  For example, 23-089E2 is a 
16k-bit TU-58 firmware ROM (E2=2Kx8 MOS) while 23-089E8 is part of a 
MicroVAX 3100 boot ROM set (E8=128Kx8 MOS).


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