RF11 disk controller

The RF11 controller from DEC for the UNIBUS is an early secondary storage controller for the PDP-11. It can interface with up to eight RS11 fixed-head magnetic disk drives; each has a capacity of 512 Kbytes of storage.

Unlike all other DEC disk controllers, the RF11 can read or write individual words; this was itended to allow optimal use of both disk space and main memory (e.g. during swapping).

Like many of the early large peripheral controllers for the PDP-11, it was a large custom wire-wrapped backplane which bolted into the front of a 19 inch rack, such as an H960; into it plugged about 40 small M-Series FLIP CHIPs.

Device registers

Register	Abbreviation	Address
Disk Control Status Register	DCS	777460
Word Count Register	WC	777462
Current Memory Address	CMA	777464
Disk Address Register	DAR	777466
Disk Address Extension Error Register	DAE	777470
Data Buffer Register	DBR	777472
Maintenance Register	MA	777474
Address of Disk Segment Register	ADS	777476

777460: Disk Control Status Register (DCS)

Error	Freeze	Write Check	Data Parity	NXD	Write Lockout	Missed Xfer	Disk Clear	Control Ready	Interrupt Enable	Ext Mem		Maintenance	Function Register		Go
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777462: Word Count Register (WC)

WC15 <---> WC00
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777464: Current Memory Address Register (CMA)

BA15 <---> BA01															Unused
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777466: Disk Address Register (DAR)

Track Address					Word Address
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777470: Disk Address Extension Error Register (DAR)

Address Parity	Timing Track Error			Unused	NXM	Unused	Current Memory	Data Req Late	Unused	Disk Addr Ovflo	Disk Address			Track Address
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

The low five bits of this register are actually an extension to the Disk Address Register (above).

777472: Data Buffer Register (DBR)

DB15 <---> DB00
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777474: Maintenance Register (MA)

Unused			Data	Timing			Unused	Data Track		Timing C		Timing B		Timing A
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777476: Address of Disk Segment Register (ADS)

Unused					Disk Segment Address
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00