RF11 disk controller

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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 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