Problem with DEC LSI11 / KD11-F

On 29/11/2014 23:03, Mattis Lind wrote: 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). -- Pete