Board NEDONAND-16 tested

A project log for NEDONAND homebrew computer

NEDONAND is 8-bit homebrew computer entirely built out of many 74F00 chips (2-input NAND gates)

SHAOSSHAOS 04/05/2016 at 04:362 Comments

Finally I completely built and tested NEDONAND-16 board that is MPROM (Manually Programmable Read Only Memory ;)

It's programmable by inserting diodes into holes in proper places:

In order to do that diode's terminals must be specifically formed:

I connected it to my Analog Discovery 2 and tested its limits in terms of frequency:

So this is 100 kHz:

And this is 1 MHz - should be good enough for TTL:

P.S. But I redo this board anyway, because couple wires still may short on some copies of the board...


Taz8du29 wrote 05/13/2016 at 19:31 point

Nice work !

Why did you use diodes ? wasn't simpler, cheaper and space saving to use dip switches ? Or it was a personnal achievement ?

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SHAOS wrote 05/13/2016 at 20:13 point

Switches will allow current to flow in both directions, but ROM in this circuit will work properly only if current flows only in one direction, so it has to be a diode, not wire

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