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Memory cores: first experiments

A project log for ED-64: A discrete 8-bit computer

ED-64 will be an 8-bit computer built with discrete components, and will feature a ferrite core memory (documented as a separate project).

andrew-starrAndrew Starr 02/16/2016 at 09:170 Comments

First off, I ought to point out that I'm far from the first hobbyist to experiment with memory cores. Here are a couple of pages I've found very useful:

Wayne's Tinkering Page

Andrew Holme's Page

Ferrite Core Memory Reborn

And of course, a moment's googling will yield a wealth of further historical and technical information.

I lashed together a couple of H-bridges to drive the select lines for a single core in the core plane, and a sense amplifier to pick up the switching transitions:

The H-bridges are pretty rudimentary, here's the schematic:

The sense amplifier is a tweaked version of Wayne's:

The above amplifier is the end product of some extensive experimentation. It has a relatively clean output, which I think I'll be able to feed into my logic 'as is' without any further gating for noise immunity.

I set up an arduino to drive the H-bridges to continuously write a '1' to a core followed by a read. Here's a scope capture of the sense coil signal (measured over a 470R resistor terminating the pulse transformer secondary):

The big spikes are the core transitions as the magnetic orientation flips back and forth. The smaller blips are artifacts caused by the magnetic fields generated by the select line currents themselves.

And finally, here is a scope capture of the output of the sense amplifier (orange trace), with the corresponding sense coil signal (blue trace):

As you can see, each core transition results in a negative-going pulse. I should be able to feed this output straight into, say, the clock input of one of my D-type flip-flops (although I haven't tried yet).

Next:

- check sense amp output can drive logic

- test functionality of inhibit coil

- extend prototype system to be able to drive every core in the plane

- further extend prototype system to be able to drive multiple planes in a 'stack'

Lots to do!

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