MSV11-Q QBUS memory

The MSV11-Q (M7551) is a quad-height QBUS DRAM main memory card. Initially it used 64Kx1 DRAM chips, later ones uses 256Kx1 DRAMs. The memory is arranged as 8 banks, each 16 data bits (1 PDP-11 word) wide, with 2 additional bits for parity (1 per byte).

It holds 1 MByte with 64K DRAMs; 4 Mbytes when fully populated with 256K DRAMs, or 2 Mbytes when half-populated (the only partially-filled configuration allowed). Three versions exist:

• MSV11-QA, 1 Mbyte (64K DRAMs)
• MSV11-QB, 2 Mbytes (256K DRAMs)
• MSV11-QC, 4 Mbytes (256K DRAMs)

all are Q22, and support block mode. The -QA comes in two etch revisions; the latter version supports battery backup. The -QB and -QC are the same etch as the later -QA.

Control Register

Each board has a single control register, which can be configured in the range 172100-172136.

In the register contents (below), all the bits can be read and written by software; most are cleared by power up and bus INIT. Bits which can only be modified by the CPU are shown in normal font, and those which can also be set by the hardware in italics.

Parity Error	Extended Error Address Enable	Reserved		Error Address							Reserved		Write Wrong Parity	Reserved	Parity Error Enable
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

The 'Error Address' field contents depend on the setting of the 'Extended Error Address Enable' bit; when it holds the low address ('Extended Error Address Enable' is 0), it holds address bits 11 through 17; when it holds the high address ('Extended Error Address Enable' is 1), it holds bits 21 through 18 - bits 11-9 of the register are unused.

Technical information

As far as is known, there are no copies of the engineering drawings extant for the MSV11-Q.

Further reading

• MSV11-QA, MSV11-QB, and MSV11-QC Field Maintenance Printset (MP-01931)