National Semiconductor NS23C 1MB memory cards

Noel Chiappa jnc at
Sat Nov 22 16:45:41 CST 2014

So I have a couple of National Semiconductor 1MB QBUS memory cards, NS23C's.
They have a _ton_ of configuration jumpers.

I have located a technical manual for the NS23C, _but_, reading it, it seems
it only applies to the 256KB version of this board.

(It's definitely a 1MB version; the memory chips are KM41C256P, 256Kx1,
and there are 36 - 4 bytes wide, with parity, so 1MB total. And there are
tons of hits on Google for NS23C 1MB boards.)

Does anyone happen to know how the 256K and 1M versions differ, if at all,
jumper-wise? I can probably work it out (maybe there a couple of extra jumpers
for the size, unless they simply multiplied the size settings by 4 - quite
possible), but it would be not too useful to expend the effort if someone else
already knows the answer.


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