ExpandaCore 18 core memory

Göran Axelsson axelsson at acc.umu.se
Mon Jul 25 18:15:48 CDT 2016

Den 2016-07-25 kl. 14:37, skrev Camiel Vanderhoeven:
> Op 25 jul. 2016 2:25 p.m. schreef "Göran Axelsson" <axelsson at acc.umu.se>:
>> My guess so far is that there is a problem with reading and writing to
> the memory. The problem is that I have no documentation over the memory
> module except a drawing of the circuitry used to access it. ND bought
> several different models of core memory for it's early computers and just
> adapted the interface.
>> So once again I turn to the cctech for help, does anybody have
> instructions about ExpandaCore 18 from by Cambridge Memories INC, Newton,
> Massachusetts (also known as CMI but probably not the CMI on bitsavers).
>> So far the only thing I've found was a newsflash in a computer magazine
> about a sale of memories to another computer maker.
> I can't help you with that, but is it just the core stack itself you don't
> have docs for, or does the CMI part include some driver circuitry? If it's
> just the stack, you should be able to do without docs for that. Core memory
> doesn't go bad unless it's physically damaged. If it is physically damaged,
> repair can be very difficult, depending on the diameter of the cores.

Thanks for the answer.

The ExpandaCore 18 (tm) ;-) is a unit with the driver electronics and 
core memory together. One control board per four memory planes and dual 
ported so a high speed device could write straight into the core memory 
without going through the CPU. In my case it seems like I have a packet 
drive interface that uses the second channel.

I have put up some more pictures here : 

Maybe I'm jumping to conclusions here but there is one "control board" 
for each four core planes. Maybe it's just a buffer. A problem with the 
core memories is that it sits tight in a crate and I have no extender 
for these cards. At least I should be able to measure the signals from 
the CPU to the control board, and from the control board to the memory 

> How are you troubleshooting this? Can you deposit a value in memory from
> the front panel, then read it back? If that works, but one or more bits are
> off, there's a good reason to look at the core driver circuitry. If it
> doesn't work at all, the problem could be anywhere. Try hooking a logic
> analyzer to the address and data lines, clock, and read/write control lines
> for a start.
> Good luck!
> Camiel

I can deposit a value in the address register (R) but that is as far as 
I have come right now. I can also look at the other registers. I think 
that the memory content should show up when I enter an address but I get 
back the same value as I entered.
The operators panel is a bit broken down, there are a couple of bad 
switches but new ones is in the mail. Some keys react on vibrations.
At the moment I can't do any measurements on the CPU-cards as there are 
no space in that crowded rack. But yesterday I cadded an extender for 
the NORD-1 CPU crate so in a week I'll be able to do some measurements 
on that part at least.

I got a cheap USB-connected logic analyzer and a digital sampling 
oscilloscope, so with the extender cards I will be able to measure or 
break up and inject any signal I want in the CPU.

This is too fun to be healthy! :-)


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