RK611 disk controller

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The RK611 disk controller is the UNIBUS device controller for the RK06 and RK07 moving-head magnetic removable cartridge disk drives. All data transfers are done using DMA. Data is protected with a hardware-generated and checked error-correcting code (ECC); corrections (up to 11 bits) are done in software.


The RK611 consists of a specially wired 9-slot backplane and five hex cards; these are:

An M7904 card, showing the connector to the drive
M7900 UNIBUS interface module
M7901 Register module
M7902 Control module
M7903 Data module
M7904 Drive interface module

At least three of the other slots are wired as UNIBUS SPC slots (and thus require G727 grant continuity cards to be inserted when no device is plugged into them); the status of the fourth appears to be 'unused'. The quad slot on the end is necessarily a plain SPC slot; the other hex slots are apparently MUD slots.

One RK611 can control up to 8 drives; a flat cable plugs into a Berg connector on one of the cards, and runs to a transition adapter on the back of the rack. From there, a round cable runs to the first drive, and similar cables connect the rest of the drives, in series. A terminator must be plugged into the 'out' port of the last drive in the series.

Backplane layout

Board locations (as seen from the board insertion side of the backplane, not the wire-wrap pin side, as is common in DEC documentation) are:

Slot A B C D E F
4 M7904 Drive interface
5 M7903 Data
6 M7902 Control
7 M7901 Register
8 M7900 UNIBUS interface
9 UNIBUS Out Unused?


The RK611 has no less than fifteen registers:

Register Abbreviation Address
Control and Status Register 1 RKCS1 777440
Word Count Register RKWC 777442
Bus Address Register RKBA 777444
Disk Address Register RKDA 777446
Control and Status Register 2 RKCS2 777450
Drive Status Register RKDS 777452
Error Register RKES 777454
Attention Summary and Offset RKAS 777456
Desired Cylinder Register RKDC 777460
Data Buffer Register RKDB 777464
Maintenance Register 1 RKMR1 777466
ECC Position Register RKECPS 777470
ECC Pattern Register RKECPT 777472
Maintenance Register 2 RKMR2 777474
Maintenance Register 3 RKMR3 777476

The addresses given assume the standard base address (0777440); if this is changed, so will the addresses. Note also that there is no register at 777462.

External links