RK11-C disk controller

The RK11-C is the earliest known version of the RK11 disk controller. (Nothing is known of the -A and -B, if they ever existed as products, although see here for more about the RK11-C's predecessor.)

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

The backplane is wired for connection to a standard DEC indicator panel, but no inlay for such has even been sighted, although the RK11-C Engineering Drawings allow one to work out exactly what such an inlay would have looked like. It does however appear than the earlier version did have such an indicator panel.

Double Buffered RK11-C

RK11-C-DB data paths (from the last page of the engineering drawings)

There is also a rare variant of the RK11-C, the 'Double Buffer' RK11-C. It adds two 16-bit buffer registers (ABUF and BBUF), which are chained in an alternate data path to the RKDB buffer register from the two sources that can feed it (the UNIBUS and the DSB - Disk Serial Buffer, where data to/from the disk is serialized).

The motivation is not explicitly known (no documentation other than the engineering drawings is now extant), but it likely prevented under-run/over-run errors when there was considerable competing UNIBUS DMA traffic.

Engineering drawings

The engineering drawings for the Double Buffer RK11-C are very similar to those of the standard RK11-C. The differences are listed below.

(The engineering drawings available online for the original RK11-C have slightly different numbering for some pages, due to a change involving page 18, 'Disk Cable and Termination'. The Double Buffer set includes that page, but numbered it 21. The re-numbering of that first drawing from 18 to 21 caused the prints numbered from 19 to 21 in the original RK11-C set to be numbered one lower in the Double Buffer set; e.g. 'RKDB Data Paths' was 21 in the original RK11-C set, and is 20 in the Double Buffer set, and 'Bus "D" Drvrs and Rcvrs' changed from 19 to 18.)

New prints:

• 24 - DSB/Bus -> ABuf Controls
• 25 - ABuf/BBuf Reg
• 26 - Interbuffer Transfer Control
• 27 - Buffer Control

Major changes:

• 10 - RKDB and Control
• 11B - Reg Sel, NPR & Int Control

Minor changes:

• 13 - Adder Control (Adder Control #2 flop set input logic)
• 15 - RKBA - RKWC - RKMR (logic lower left corner)
• 16 - Errors (logic center driving DLT flop)
• 17 - Cable Drivers (hand-written gate lower left)
• 20 - RKDB Data Paths (replace 'BUS D' with 'BBUF' on all data bits)

Module count table

The following table gives a listing of the FLIP CHIPs used in the RK11-C and the Double-Buffered RK11-C. (Drawn from module utilization drawings, confirmed in module count charts.)

Single height boards:

Type	RK11-C	Double-Buffered	Function
G736	1	1	Jumper
G740	1	1	Disk selection
M002	1	3	15 Loads
M105	1	1	Address selector
M111	2	5	Inverter
M112	5	7	NOR gate
M113	7	10	10 x 2-Input NAND gates
M115	3	4	8 x 3-Input NAND gates
M116	3	3	6 x 4-Input NOR gates
M117	3	4	6 x 4-Input NAND gates
M119	2	2	3 x 8-Input NAND gates
M121	3	3	AND/NOR gates
M141	2	2	NAND/NOR gates
M149	10	12	9 x 2-NAND wired OR matrix
M161	1	1	Binary to octal/decimal decoder
M163	1	1	Dual binary to decimal decoder
M203	4	4	8 x SR flip-flops
M205	3	4	5 x 'D' flip-flops
M207	1	1	J-K Flip-flops (3-3 configuration)
M208	2	6	8-bit buffer shift register
M214	3	3	6-bit register
M216	5	5	6 x flip-flops
M236	1	1	12-bit binary up/down counter
M238	1	1	Synchronous 4-bit up/down counter
M239	2	2	3 x 4-bit up/down counter/register
M304	3	5	One shot delay
M307	3	3	Integrating one shot
M405	1	1	Crystal clock
M606	0	2	Pulse generator
M611	1	1	High speed power inverter
M617	1	1	6 x 4-input NAND buffers
M623	3	3	Bus driver
M782	1	1	Interrupt control
M784	3	3	UNIBUS receivers
M796	1	1	UNIBUS master control
M797	1	1	Register select
M798	1	1	UNIBUS drivers

Double height boards:

• M795 - Word Count and Current Memory Address

Module Utilization chart

The following table gives the FLIP CHIP locations in the backplane for the RK11-C and the Double-Buffered RK11-C (added FLIP CHIPs for the latter are in italics). The Flip Chip module utilization chart is as follows (* = Connector):

Slot	A	B	C	D
1	UNIBUS in		M606	M113
2	UNIBUS out		M115	M002
3	M149	M149	M208	M208
4	M111	M002	M205	M113
5	M105	M784	M208	M208
6	M782	M796	M304	M304
7	M795		M606	M112
8	M784	M784	M112	M111
9	M117	M111	M623	M307
10	Disk bus 2*		M623	M307
11		M113	M623	M307
12	Disk bus 1*		M207	M163
13	M798	G736	G740	M405
14	M149	M149	M116	M161
15	M149	M149	M304	M119
16	M149	M149	M113	M113
17	M239	M238	M216	M141
18	M239	M214	M115	M115
19	M214	M214	M121	M112
20	M208	M208	M111	M111
21	M203	M203	M112	M112
22	M149	M149	M205	M117
23	M149	M149	M203	M203
24	M121	M002	M116	M115
25	M216	M797	M611	M617
26	M141	M119	M113	M304
27	M304	M112	M112	M113
28	M236	M121	M216	M216
29	M205		M117	M117
30	W130*		M113	M113
31	6775*		M113	M205
32	6775*		M116	M216

W130 = Maintenance board (optional)
6775 = Cable to indicator panel

Documentation

• RK11-C manual, 1971
• RK11-C schematics, February 1971
• RK11-C-DB Double Buffer Disk Control Engineering Drawings, December 1972