Core memory emulator using non volatile ram.

[Rod G8DGR]

Sent from Mail for Windows 10

From: allison via cctech
Sent: 16 December 2018 03:08
To: cctech at classiccmp.org
Subject: Re: Core memory emulator using non volatile ram.

On 12/15/2018 01:01 PM, Guy Sotomayor Jr via cctech wrote:
> FRAM or MRAM.  I make extensive use of them in my projects.
>
> Everspin has a few (all SMT and 3.3v).  As I recall they run ~$20/ea for 4Mb (512K x 8 or 256K x 16).
>
> TTFN - Guy
>
>> On Dec 15, 2018, at 1:22 AM, Rod G8DGR via cctalk <cctalk at classiccmp.org> wrote:
>>
>> I have an idea to produce an MM-8  clone using RAM that acts like core when turned off.
>> Can anybody suggest a chip that will do this?
>>
>> Rod Smallwood
>>
>>
My call on this is that cmos static ram 4Bit wide does the job well I
have 32K of it in my PDP-8 to
get past possible failure of hard to find and get core.  A Panasonic
BR-1 lithium cell has enough
capacity at the measured drain for about 6-7 years and the Dallas power
management chip
makes it a non hack.  Flash, EEprom and Magnetic FRAM and MRAM) types
have many unacceptable
properties for a random access read write memory.  It makes no
difference to the PDP8(ILEFMA)
that read is not destructive as it will write back as needed anyway.

There is a design on the 'net for using CMOS ram in a straight forward
buildable array for Omnibus
with battery back up that is fine.  Don;t get wraped around the axle
about RMW as any sufficiently
fast ram can do that without wearout.  And compared to core it doesn't
take much speed.

EEprom and Flash work fine for read mostly disks or disk simulators.

Allison

Sheesh!! Well what a response. 
This stems from my (so far) successful major over haul of my PDP-8/e.
I found one failed 7474 and one failed 8881 – replaced and now working.
I think I have the rim loader toggled in and will attempt to send a paper tape image from Hyperterm
Strangely I do have at least three genuine complete 4k memory sets.

However I began to think would it be possible to create a close copy of an  8/e out of  modern parts.
As you all know I make front panels so that’s not a problem. 
I did manage to copy my (distorted) bezel in resin.
A friend has been able to 3D print toggle switch leavers that fit and work.
Vince Sylngstat has done a console board PCB  layout.
Power supply clearly not a problem.
So what’s left? Case?  
Well I have one of those and I suspect a sheet metal shop would not have a problem

Finally the big one – Omnibus and the connectors its made from. A 3D printing candidate?
I’m going to autopsy a busted connector and see how they are constructed inside.

Objectives
The basic board set as original. M8300, M8310, M8320 etc.
Same form factor
Plug compatible – but board contents can differ from original

The idea is replace one item at time until you no longer have any DEC parts.
Yup a FAKE-8

I may even need a label “No part in this PDP-8/e computer was manufactured by digital equipment corporation”

Rod Smallwood