View source for MS11-M MOS memory

[[Image:MS11-M.jpg|300px|thumb|right|MS11-M board]]

The '''MS11-M''' ('''M8722''') is a [[Metal Oxide Semiconductor|MOS]] [[Dynamic RAM|DRAM]] [[main memory]] card; it can theoretically be configured as either [[UNIBUS]] memory, or [[Extended UNIBUS]]. In actuality, the MS11-M uses power [[voltage]]s of +12V/-12V, unlike the normal +15V/-15V supplied by most DEC [[backplane]]s, and thus can be used in only a few installations.

When configured for UNIBUS use, it is plugged into an [[Modified UNIBUS Device|MUD]] [[backplane]] slot. '''''Note:''''' a MUD slot does not usually provide +12V/-12V; in general, the MS11-M thus cannot actually be plugged into most MUD backplanes.

When configured as an EUB card, it can only be plugged into the EUB slots on the backplanes of the [[PDP-11/24]] (in the [[BA11-A mounting box]] '''''only''''') and the [[PDP-11/44]], which provide the correct voltages. Configuration is mostly by [[Dual Inline Package|DIP]] switches, along with two [[jumper]]s.

It has [[Error-correcting code|ECC]] which automagically corrects single-[[bit]] errors, (at a 70 nsec penalty in [[access time|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.

The [[access time]] is normally 490-525 nsec (typical/max; 620-675 nsec extra on [[memory refresh]] conflict), and the [[cycle time]] is 950-1000 nsec (write cycle; refresh conflict additional as above). Refresh time is 620 nsec (typical; 675 nsec maximum); the time for a complete refresh pass is 12.5 μsec (typical), or 13.75 μsec (maximum).

It is a [[DEC card form factor|hex-height]] card; the '''MS11-MB''' holds 256 Kbytes when fully populated with 16Kx1 DRAM [[integrated circuit|chips]]; the half-populated '''MS11-MA''' contains 128 Kbytes.

==Power==

Power requirements are 3.8-4.8A of +5V; 1.2-1.5A of +5VBB; 25-50mA of -12V, on pin AS1 (depending on size, i.e. number of MOS memory chips); and .55-1 A of +12V, on pin AR1 (when active; depending on size). Note that if two MS11-M boards are [[memory interleaving|interleaved]], the +12V current draw can be doubled.

The board has provision to use battery backup power to retain data during a power outage.

==External links==

* [http://bitsavers.org/pdf/dec/pdp11/1144/EK-MS11M-UG-001_UsersMan_May79.pdf MS11-M MOS memory user guide] (EK-MS11M-UG-001)
* [http://bitsavers.org/pdf/dec/pdp11/1144/MP00897_11X44sys_Dec79.pdf 11X44 Field Maintenance Print Set] - the MS11-M Field Maintenance Print Set (MP00742) is on pp. 238-282

[[Category: UNIBUS Memories]]
[[Category: EUB Memories]]