National Semiconductor NS23M QBUS memory
From Computer History Wiki
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.
