MSV11-R memory module

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MSV11-R card

The MSV11-R (M7458) is a quad-height QBUS/PMI DRAM main memory card.

NOTE: As a PMI card, it uses the CD interconnect; it can therefore only be plugged into a Q/CD backplane. Plugging an MSV11-R card into a regular Q/Q backplane will damage the MSV11-R.

The MSV11-RA (M7358-A) holds 1 MByte when fully populated with 256K DRAM chips. The memory is arranged as 2 banks, each 16 data bits (1 PDP-11 word) wide, with 2 additional bits for parity (1 per byte). In theory, it could support being half-populated (512 Kbytes), with only one bank; there is a jumper, W1, which seems to support this configuration, but no documentation for it. It is not clear if DEC ever sold that configuration.

It is a Q22 card; it also supports block mode (with a maximum block size of 16. words, depending on the block's start address).


A single 8-position DIP switch configures the card:

  • Switches S1-S2 sets bits 21-20 of the board's 22-bit starting address;
  • DEC documentation asserts that switches S3-S4 must always be off; however they seem to be functional (although perhaps only for the single bank configuration), and set address bits 19-18;
  • Switches S5-S8 select the CSR address.
S1 S2 Staring Address
OFF OFF 00000000 (0 MB)
OFF ON 04000000 (1 MB)
ON OFF 10000000 (2 MB)
ON ON 14000000 (3 MB)

Control Register

Each board has a single control register, which can be configured in the range 17772100-17772136.

S5 S6 S7 S8 CSR Address
ON ON ON ON 17772100
ON ON ON OFF 17772102
ON ON OFF ON 17772104
ON ON OFF OFF 17772106
ON OFF ON ON 17772110
ON OFF ON OFF 17772112
ON OFF OFF ON 17772114
ON OFF OFF OFF 17772116
OFF ON ON ON 17772120
OFF ON ON OFF 17772122
OFF ON OFF ON 17772124
OFF ON OFF OFF 17772126
OFF OFF ON ON 17772130
OFF OFF ON OFF 17772132
OFF OFF OFF ON 17772134
OFF OFF OFF OFF 17772136

Technical information

A copy of the engineering drawings for the MSV11-R has recently been discovered, in a set of PDP-11/84 engineering drawings (see link below). As described above, each board has 2 banks in the array of DRAM chips; with 256K chips, each bank is thus 512KB. The chips in each bank run across the board (when it is oriented with the chip side facing the viewer, with the metal edging holding the handles at the top). Bit 0 (value 1) of the even byte of the low bank is on the right hand edge of the top row of the array; bit 15 (value 0100000), the top bit of the odd byte, is toward the left hand side of the second row. The two parity bits are on the extreme left hand edge. The high bank is in the third and fourth rows down the board from the metal handle edge. The full bit<->chip table is:

Bit Bank 0 Bank 1
01 E76 E78
02 E83 E85
04 E90 E92
10 E94 E96
20 E101 E103
40 E108 E110
100 E114 E116
200 E121 E123
400 E75 E77
1000 E82 E84
2000 E89 E91
4000 E93 E95
10000 E100 E102
20000 E107 E109
40000 E113 E115
100000 E120 E122
Low byte Parity E128 E130
High byte Parity E127 E129

The following 256K DRAM chips have been observed to be used: MB81256-15 (Fujitsu).

Further reading

  • MSV11-R User Guide, EK-MSV1R-UG

External links