MM11-L core memory
The MM11-L core memory was a popular, and common, 16 Kbyte core main memory unit for the early PDP-11 UNIBUS machines. An MM11-L was composed of a three board set:
- G110 - hex-width memory control logic and data channels
- G231 - hex-width memory driver logic
- H214 - quad-width core stack
The MM11-L required a custom backplane, although some CPU's (e.g. the PDP-11/05) had processor backplanes wired to hold one or more MM11-L sets, as well as the CPU.
There was also a parity variant, the MM11-LP, which added an M7259 dual-width parity controller, and substituted an H215 (with two more bits per word) for the H214, and a G109 for the G110. Enabling parity increased the access time from 400 nsec to 525 nsec.
The MM11-S was a four-slot backplane plus a single MM11-L board set. The MF11-L was a nine-slot backplane plus a single MM11-L board set; the backplane has room for two more MM11-L board sets. The ME11-L was an MF11-L in a 5-1/4" rack-mount box, with power supply (the -LA was wired for 115V supply, the -LB for 230V).
Parity versions (with a 'P' suffix) were available for all of the above. The manual indicates that an 'MF11-LP backplane' was required, but it is not stated if this version had a different PCB, or if the non-parity version simply had a jumper, like the MM11-U core memory.
The explanation appears to be that there are two versions of the backplane, the early one (part #5409959) which cannot run parity, and a later one (part #5410331) which can. An example of the later backplane had the same jumper as that called for for the MM11-U, from pin B1U1 to B2U1, which appears to confirm this analysis.
This jumper should not be present for parity memory. Note that therefore parity and non-parity memory cannot be mixed on the same backplane. There is also no provision for use of the M7259 parity controller in the PDP-11/05 backplanes which support the MM11-L.
The board organization in the MM11-L backplanes is not given in the manual; that for the MF11-L is:
| Connector | ||||||
|---|---|---|---|---|---|---|
| Slot | A | B | C | D | E | F |
| 1 | UNIBUS In | H213/H214 Core stack | ||||
| 2 | G231 Memory Driver | |||||
| 3 | G110 Memory Control | |||||
| 4 | G231 Memory Driver | |||||
| 5 | G110 Memory Control | |||||
| 6 | M7259 Parity Controller | H213/H214 Core stack | ||||
| 7 | G231 Memory Driver | |||||
| 8 | G110 Memory Control | |||||
| 9 | UNIBUS Out | H213/H214 Core stack | ||||
The first MM11-L set goes in slots 1/2/3; as MM11-L sets were added, they were installed in slot numerical order. The location of the parity controller has yet to be definitively documented, but there is only one open dual slot in a full MF11-L.
