Looking for info on memory

[Jerry Weiss]

On 10/20/21 12:27 PM, Douglas Taylor via cctech wrote:
> On 10/19/2021 12:57 PM, Nigel Johnson Ham via cctech wrote:
>> I am trying to bring up an 11/23 system in a BA23 box, and the only
>> memory i have is an obscure Plessey one. The only identification is the
>> p/n 705920 with dash-100 in white ink. By counting the chips I make it
>> 4MB, but it does not respond. Since it takes the full 22-bit memory
>> space I can't see how any jumpers would change its accessibility. Does
>> anybody have a manual?
>>
>> any help appreciated,
>>
>> Nigel Johnson
>>
> Looking at the photo I began to wonder if Plessey made their own 
> boards or are they re-badged from some other manufacturer.   I don't 
> know.  If they are made by someone else, you might be able to dig up a 
> manual.
>
> Also, if you look at the documentation for other 4MB qbus memories how 
> many jumpers do they have?  And what do they do?  It may help you 
> understand your board.
>
> Doug  (of course I don't have a 4MB qbus memory, but that apparently 
> didn't stop me from posting.)
>
Looking at the silk screening, there is a Plessey logo so this is mostly 
likely there own design.   Given the date on warranty I would expect 
jumpers for 18/22 bus type, perhaps battery backup, parity CSR, memory 
chip size, I/O page size,etc...   But assuming the jumpers for memory 
address start and length are in some functional configuration, you 
should to poke/read ODT somewhere in the 4MByte addressing range.   You 
might also try to see you can read  default parity CSR for memory 
boards. The logic (and some circuity) for I/O page should be different 
than memory decoding.
Suggest you obtain a another memory board (e.g. M8044) to verify the 
other components.


Jerry