MS11-M MOS memory

The MS11-M (M8722) is a DRAM main memory card; it can be configured as either UNIBUS memory, or Extended UNIBUS.

When configured for UNIBUS use, it is plugged into an MUD backplane slot. Note: The MS11-M uses power voltages of +12V/-12V, unlike the normal +15V/-15V supplied by an MUD/SPC slot. In general, the MS11-M thus cannot actually be plugged into most MUD/SPC backplanes.

When configured as an EUB card, it can only be plugged into the EUB slots on the PDP-11/24 or PDP-11/44 backplanes (both of which provide the correct voltages).

It is a hex-height card; the MS11-MB holds 256 Kbytes when fully populated with 16Kx1 DRAM chips; the half-populated MS11-MA contains 128 Kbytes.

It has ECC which automagically corrects single-bit errors, (at a 70 nsec penalty in response time when an error occurs) and detects double-bit errors. The memory is arranged as 4 banks, each 32 data bits wide, with 7 additional bits for the ECC.

On power-on, the system is frozen (via negation of the ACLO UNIBUS signal) for up to 451 msec while the entire 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.