MSV11-J memory module

The MSV11-J (M8637) is a QBUS/PMI DRAM main memory card. As a PMI card, it uses the CD interconnect; it can therefore only be plugged into a Q/CD backplane. NOTE: Plugging an MSV11-J card into a regular Q/Q backplane will damage the MSV11-J.

It has ECC which automagically corrects single-bit errors (at a slight penalty in response time), and detects double-bit errors. It holds up to 2 Mbyes when fully populated with 256Kx1 DRAM chips, or 1 Mbyte when half-populated (the only partially-filled configuration supported). It supports block mode on both the QBUS and PMI.

Although it can function in QBUS-only mode (but see the note below about the -JB and -JC versions), it is really intended for use with a PMI-capable CPU, such as the KDJ11-B. In systems such as the PDP-11/83, where the primary I/O bus is the QBUS, the card 'speaks' PMI to the CPU, and QBUS to the devices. In the PDP-11/84, the PMI is used for communication with both the CPU and the KTJ11-B UNIBUS adapter.

The memory is arranged as 2 banks, each 16 data bits wide, with 6 additional bits for the ECC. One bank is used to hold words at even locations, the other for those in odd; a read cycle from the bus will read both sides simultaneously, and so when in PMI mode, the second word is already available once the first has been sent.

On power-on, the system is frozen (via negation of the BPOK QBUS signal) while the memory is cleared, to prevent spurious ECC errors. For diagnostic purposes, the ECC can be disabled, and there are also means for the CPU to read/write the ECC bits directly.

Four versions exist:

• MSV11-JB, 1 Mbyte
• MSV11-JC, 2 Mbyte
• MSV11-JD, 1 Mbyte
• MSV11-JE, 2 Mbyte

The -JB and -JC are earlier versions which contain an error which prevents them working properly as QBUS memories (i.e. in the PDP-11/83); they are only usable in the PDP-11/84.

Markings

On the board

M8637
Side 1
L1
50-15672-01 C1
Ga6618
2644711
2 MB Q,P-BUS MOS MEM
LPWR
TPB
D.V0

On the metal frame

P/N 1213113
M8651
EC
ASICs on board are 21-24404-01 and 21-22772-01