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).

Identification

Unlike the NS23C, the NS23M printed circuit board does not contain any identification which indicates directly that it is an NS23M. The PCB only says "PWB 551103882-003" and "PWA 980103882", both on the component side; one often sees these boards listed on auction sites under these ids.

Configuration

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

Size

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.