M7259 Parity Control Module

The M7259 Parity Control Module is an optional accessory for the parity versions of the MM11-L and MM11-U core memory main memory systems on the UNIBUS; it is needed for them to actually provide the parity protection.

It provides byte parity. Memory access time on read is increased by 125 nsec if parity is enabled. Cycle time on write is not affected if parity is enabled. On later revisions of the M7259, if an error occurs, an LED on the end is illuminated.

The M7259 is a dual format card, which plus into a dedicated slot of the MF11-L/MM11-U backplane into which the associated memory unit(s) are plugged. Parity, and the M7259, is thus not supported for MM11-L/MM11-U units in a PDP-11/05 CPU backplane.

The M7259 requires slightly different backplane wiring for parity memory from non-parity. One M7850 can provide parity support to as many memory units as the backplane holds (3 for the MM11-L; 2 for the MM11-U).

Control and Status Register

The M7259 has a single register to control and monitor its operation. Its address may be set in the range 0772100-0772136 by a group of jumpers on the M7259. Its format is:

ParErr	Unused			ErrAddr							Unused		WrWrong	Unused	SignalErr
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Errors are not signaled to the CPU unless bit 0 is set. After an error, the ErrAddr field contains the highest-order address bits (A17-A11) of the location which produced the error. All bits can be written by the CPU; all except the Error Address are cleared by the INIT bus signal.

See also

• UNIBUS parity

External links

• MM11-S, MF11-L, and MF11-LP core memory systems (DEC-11-HMFLA-C-D) - the M7259 is covered in Appendix A
• MF11-U/UP memory system engineering drawings - the M7259 is covered on pp. 7-40 of the PDF