National Semiconductor NS23M QBUS memory

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The National Semiconductor NS23M is a QBUS memory card in dual QBUS card-size format. It can be configured to use either 16Kx1, 32Kx1 or 64Kx1 DRAMs, operating at 150nsec or 200nsec; it has a maximum capacity of 256 Kbyte (using 64Kx1 DRAMs).


The board is configured with a combination of jumpers and DIP switches.

Jumper(s) Function
W1-W2, W17-W18 200ns/150ns DRAM
W3-W4 Test
W5-W7, W12 16K/32K/64K DRAM
W8-W9 Test
W10-W11 Internal/External Refresh
W13-W14 32K DRAM Upper/Lower
W15 18-/22-bit QBUS (in/out)
W16 External Refresh / MEMSEL
W19-W20 Battery Backup

Starting Address

Switch Address bit
S1-1 20000
S1-2 40000
S1-3 100000
S1-4 200000
S1-5 400000
S1-6 1000000
S1-7 2000000
S1-8 4000000
S1-9 10000000


Jumper(s) Function
S2-1 16KB
S2-2 32KB
S2-3 64KB
S2-4 128KB
S1-10 2K/4K I/O Address Space (closed/open)

Note that the size is the value indicated, plus 16KB (the minimum); i.e. 0000 = 16KB, 1111 = 256KB.