Problem with DEC LSI11 / KD11-F

Mattis Lind mattislind at
Sat Nov 29 17:03:14 CST 2014

lördag 29 november 2014 skrev Pete Turnbull <pete at>:

> On 29/11/2014 20:22, Mattis Lind wrote:
>> I have been browsing through some of my old Qbus boards and found one
>> KD11-F (M7264) CPU with 4 k word memory, a couple of KD11-HA (M7270) , a
>> KDF11-A (M8186) and some assorted memory boards and some SLUs.
>> All CPUs seemed to work except for the KD11-F board
>  The M7264 board has the following chips:
>> CP1611B-51  2111549
>> CP1621B451  23001C201
>> CP1631B-10   23088A501
>> CP1631B-07   23087A501
>> The M7270 board has the following chips:
>> 1611H  21-15579
>> 3007D  23-002B5
>> 3010D   23-001B5
>> 2007C   23-002C4
> As far as I knew, they used the same chipset with the same instruction
> set, but those are clearly different.  The 21-15579 is the ALU etc, the
> 23-xxxxxx are the microcode ROMs.  Obviously you could swap the 21-15579,
> but you probably can't mix-and-match the ROMs.  It couldn't be that one set
> is something other than a PDP-11 instruction set?
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 anyone have a spare 23088A5 chip, maybe?

> --
> Pete

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