RK11 disk controller

The RK11 and RKV11 series of controllers for the UNIBUS and QBUS are for the earlier RK moving-head magnetic disk drives (RK02-RK05), all based on the IBM 2315 drive and pack.

(The later RK06 and RK07, and their controller, the RK611, are a different and entirely incompatible drive and pack.)

There are several models of the RK11, which are basically identical in their programming interface; differences between them are discussed in the sections on the individual models (below).

The UNIBUS RK11's all connect to the RK drive(s) through a bus carried over a BC11A cable, the standard UNIBUS cable.

Early RK11 version

Although the RK11-C (below) is the earliest documented version, there are a few clues which indicate that there was an earlier version (one for which no documentation remains).

First, there is an image of a DEC indicator panel (image here) which seems to be from a pre-RK11-C; it clearly seems to be an RK11 panel of some sort, but the pinout of the RK11-C indicator panel connector (engineering drawing "RK11-C Indicator Connectors: RK11-C-23") has differences with this one.

In particular, on the panel in the image, the lower right line of lights on the panel shows 3 bits of Major State; on the RK11-C prints (on connector B32) there are 5 individual bits (Postamble, Checksum, Data, Header, Preamble). To explore this further, on the "Major States" RK11-C drawing (RK11-C-04), in the upper left corner, there is a row of 6 flops, each labeled with one of those states (plus one for 'Idle'), arranged in a chain - the output of each driving an individual light. However, the 3 bits for 'Major State' on the display panel imply it is binary coded - likely implemented with a counter.

Also, the signal "COUNT MSR" (likely 'Major State Register') is exactly what one would expect to see if the major state had previously been held in a counter, not a string of flops. It makes no sense to expend the effort synthesize that signal (on the next page, RK11-C-05, "MSR Control") when the individual signals which go into it could have been used, as is, to clock each flop in the chain.

A reasonable guess, in light of these facts, is that in some previous version, a counter had been used, but had had a problem of some sort, and had therefore been replaced by the string of flops. (The reason is unknown, but perhaps it was a binary counter, not Gray code, and the decoding into states was producing glitches.)

A plausible scenario is that such an earlier version was produced in very small numbers - perhaps as prototypes, only internal to DEC. (If there had been problems discovered with glitches in the major state counter, they would not have wanted to release it as a product.) Or if it was released as a product, perhaps they were all recalled and replaced with RK11-C's.

In this regard, it is interesting to note the DEC Spare Module Handbook, lists only the RK11-C and -D, but does list the KT11-B, a rara avis indeed. This argues that the predecessor did not exist 'in the wild'.

RK11-C

Main article: RK11-C disk controller

Like many of the earlier large peripheral controllers for the PDP-11, the RK11-C was a large custom wire-wrapped backplane which bolts into the front or back of a 19 inch rack, such as an H960; into it were plugged about 40 small M-Series FLIP CHIPs.

The RK11-C supports up to 4 drives per device bus (it uses 4 different 'select' lines on the bus, one of which is asserted at a time), and has two device busses.

RK11-D

The RK11-D was a re-implementation of the RK11-C on four quad cards (M7254-7), which plugged into a custom-wired 4 slot hex-high system unit backplane, for a BA11 slide-out mounting box.

It was program compatible with the RK11-C, except that the RK11-D did not contain the Maintenance Register of the earlier controller. In the RK11-D, the bus location of the MR responds, but according to the engineering drawings, it reads as zero, and written data is ignored.

The RK11-D supports up to 8 drives per device bus (it uses 3 'select' lines on the bus, with the drive number encoded in binary), and has only one device bus.

The RK11-D also has a 6-word FIFO buffer between the disk and the bus (see sheet 7 of the M7256 engineering drawings). The original RK11-C had only one word of buffering, which was probably not enough, and likely the reason for the double-buffered RK11-C version.

RK11-E

The RK11-E (sometimes called the RK15) was a variant of the RK11-D which supported 18-bit data; it was used with the PDP-15. It used the same cards as the RK11-D, with a jumper selection for 18-bit operation, and a different clock crystal.

It was used with the UC15 Unichannel, which used a PDP-11 (usually a PDP-11/05) acting as a slave to the PDP-15; the RK11-E was plugged into the UNIBUS on the PDP-11.

It used the two UNIBUS parity lines for the two extra data bits on the 18-bit PDP-15. The two extra bits were not used by the PDP-11 or its memory, but went straight through the MX15-B Memory Multiplexer, directly to the PDP-15's main memory.

RKV11-D

RKV11-D card cage and H780 power supply

The RKV11-D is a variant of the RK11-D for the QBUS (the others are all UNIBUS).

It uses three of the four quad cards of the RK11-D (M7254-6), along with a replacement fourth card (M7268), in a different custom 4 slot quad-high system unit backplane. The M7268 is connected via two pairs of flat cables to two dual cards, one of which (M7269) plugs into a QBUS backplane slot, and the other (M993-YA) into the first RK05 drive. The RKV11-D is mounted in a BA11-M style mounting box with H780 power supply. The BA11-M front panel is replaced with an expansion box front panel, with a single indicator for DCOK.

It is program compatible with the RK11-D, except that it only supports Q16 QBUS mode when writing data. The two extended memory bits in the CSR have no effect; they may be read and written, but are not connected to anything.

Device registers

Register	Abbreviation	Address
Drive Status Register	RKDS	777400
Error Register	RKER	777402
Control Status Register	RKCS	777404
Word Count Register	RKWC	777406
Current Bus Address Register	RKBA	777410
Disk Address Register	RKDA	777412
Maintenance Register	RKMR	777414
Data Buffer Register	RKDB	777416

777400: Drive Status Register (RKDS)

Drive ID			DPL	RK05	DRU	SIN	SCOK	DRY	R/W/S Ready	WPS	SC=CA	Sector Counter
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Note that in the diagram of this register in the 'peripherals handbook' (both 1975 and 1976 editions), bits 7 and 6 are labelled incorrectly; the table which lists the bits has them correctly.

(To confirm this, consult the RK11-D print set, M7254 page 3; the dual 4->1 muxes which fill this page are the source of the RKDS, RKER, etc registers.)

The name of bit 6 has changed slightly from the RK11-C to the -D ("Access Ready" to "R/W/S Ready"), but it seems to be basically the same functionality.

777402: Error Register (RKER)

DRE	OVR	WLO	SKE	PGE	NXM	DLT	RTE	NXD	NXC	NXS				CSE	WCE
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777404: Control Status Register (RKCS)

ERR	H.E.	SCP	M	IBA	FMT	R/WA	SSE	RDY	IDE	EX. MEM		FUNCTION			GO
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Bit 9 is"Read/Write All" in the RK11-C, and unused in the -D; bit 12 is "Maint" in the -C, and unused in the -D.

Command	Code	In CSR
Reset Controller	0	0
Write	1	02
Read	2	04
Write Check	3	06
Seek	4	010
Read Check	5	012
Reset Drive	6	014
Write Lock	7	016

777406: Word Count Register (RKWC)

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

777410: Current Bus Address Register (RKBA)

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

777412: Disk Address Register (RKDA)

DRIVE SELECT			CYLINDER ADDRESS								SUR	SECTOR ADDRESS
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

777414: Maintenance Register (RKMR)

M. RCP	M. RDP	M. SPS	M. ADA	M. LAI				M. DRY	M. R/W/S			MAINT. SECTOR COUNTER
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

This register is not present in the RK11-D; it reads as 0, and writes to it are discarded.

777416: Data Buffer Register (RKDB)

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

PDP-11 bootstraps

Disk 0

Address	Data	Mnemonic	Description
1000	012700	MOV #177406,R0	Move the address of the Word Count register into R0
1002	177406		(constant)
1004	012710	MOV #177400,(R0)	Move block size (negative) into Word Count register
1006	177400		(constant)
1010	012740	MOV #5,-(R0)	Move 'Read Go' command into CSR
1012	000005		(constant)
1014	105710	TSTB (R0)	Test for 'Done' bit in CSR
1016	100376	BPL 1014	Jump backward if not set
1020	005007	CLR PC	Start loaded bootstrap with jump to 0

Note that the INIT pulse caused by hitting the 'Start' button will clear the Bus Adddress register, so the loaded block will be placed at location 0.

Disk n

This bootstrap will boot from any disk in a daisy-chained multi-drive configuration. Memory location octal 1006 contains the unit number, as follows:

Address	Data	Mnemonic	Description
1000	012700	MOV #177406, R0	Store the address of the Word Count register in r0
1002	177406	(constant)	(Which is 177406)
1004	012760	MOV xxxxxx, 000004(R0)	Store the disk ID number in the Disk Address register
1006	xxxxxx	(disk ID number)	The disk number goes here.
1010	000004	(index)
1012	012700	MOV #177406, R0	Store the addresss of the Word Count register in r0
1014	177406	(constant)	(Which is 177406)
1016	012710	MOV #177400, (R0)	Store 177400 into the Word Count register,
1020	177400	(constant)	meaning that octal 400 words are to be read.
1022	012740	MOV #000005, -(R0)	Store 5 into the Control Status register
1024	000005	(constant)	selecting the function "read" with 4, and "go" with 1
1026	105710	TSTB (R0)	Test the Control Status Register (upper) byte
1030	100376	BPL *-1	Repeat if it's positive, that is Control Ready is cleared
1032	005007	CLR PC	If not, clear the Program Counter (essentially, jump to 0)

Value	Unit
020000	Unit 1
040000	Unit 2
060000	Unit 3
100000	Unit 4
120000	Unit 5
140000	Unit 6
160000	Unit 7

External links

RK11-D and RK11-E moving head disk drive controller manual (DEC-11-HRKDA-B-D)
RK11-D and RK11-E moving head disk drive controller user's manual (EK-RK11D-OP-001)
RK11-D and RK11-E moving head disk drive controller manual (EK-RK11D-MM-002)
RKV11-D disk drive controller user's manual (EK-RKV11-0P-001)
RK11-D disk drive controller engineering drawings (Rev P, 10-1975)
RK11-D Engineering Drawings (Rev R, 10-1976)
RK11-D ECOs