KA11 changes for the KT11-B

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The KT11-B Paging Option for the PDP-11/20 involves some modifications to the KA11 CPU. Those changes are documented in a DEC print set, 7605961-0, "Central Processor for KT11-B".

Alas, there's only one known set of these prints for the KT11-B changes to the KA11 - and that set is missing a page: "PC Board Modifications", D-AP-7605961-0-10.

Luckily, there is probably just duplicate information elsewhere (including a hand-modified set of KA11 prints, showing the changes to suppport the KT11-B) to allow it to be reproduced.

Print set

The following prints are included in the "Central Processor for KT11-B" set:

Drawing Sheets Title
D-CS-7605961-0-3 3 State Control - M727 K2
D-CS-7605961-0-4 3 Priority - M824 K3
D-CS-7605961-0-5 5 Bus Interface & Instruction Register - M725 K9
D-CS-7605961-0-6 4 Instruction Register Decode - M726 K10
D-CS-7605961-0-7 3 Flag Control - M822 K12
D-CS-7605961-0-8 4 Bus & Console Control - M724 K13

KA/KT Interface

The KA11 and KT11-B are connected by a single cable which carries specific signals, as well as the UNIBUS. On the KT11 end, it plugs into slot D12, and on the KA11 end, into slot B09. The cable pinout is:

Pin Source Signal  ! Pin Source Signal
A1 - Ground A2  ? xx
B1 KA11 Odd address error B2  ? xx
C1 - Ground C2 - Ground
D1 KT11 PGC 04 D2 KA11 RTS
F1 - Ground F2 - Ground
J1 KA11 ISR 12 J2 - Ground
K1 - Ground K2 KA11 SERVICE
L1 KA11 ISR 7 L2 - Ground
N1 - Ground N2 - Ground
R1 - Ground R2 - Ground
T1 - Ground T2 KA11 [ST+SR] K13-3
U1  ? xx U2 - Ground
V1  ? xx V2 KT11 Force timeout

(Signals partially in lower case are not formal names from the prints, but give a sense of what the signal does.)

KA11 modifications

An M138 FLIP CHIP (octal three-input NAND gates) is also plugged into the KA11 backplane (in slot B08, otherwise unused), to provide additional gates.

The following list of wiring changes on the KA11 backplane is drawn from print 7605961-0-11, "KA11 Mods For Use With KT11-B". All wires are listed as being 30 AWG. (Note: This print reproduced poorly, so there may be transcription errors (e.g. '8' for '3', etc.)

Wires removed

From To Signal Colour
B02T2 F08U2 K13-3 B MSYN H Orange
D12C2 D12S1 GND 12
E04K1 E07P2 K10-4 CLKT H
E03F1 E04L1 K?-2 SCLK L
D11B1 C06J1 K10-3 ODD ADRS ERR L
C06J1 D02N1 K10-3 ODD ADRS ERR L
D12S1 D12T1 GND 12 Brown

Wires added

All added wires are listed as Orange. This list had previously been checked, and annotated by hand in ink; those annotations are given here. All entries with no annotation given have a hand-written check-mark in ink.

From To Signal Comment
E03F1 F06H1 K1-2 SCLK L
Dx2C2 D12T1 GND 12 None
D11B1 D02N1 K10-3 ODD ADDRS ERR L None
xx yy K10-2 ODD ADDRS ERR L
xx yy K10-2 ODD ADDRS ERR L
xx yy K10-2 ODD ADDRS ERR L
xx yy B08D1
xx yy B08D1
xx yy K1-2 SCLK L E04L1 - B08M1
xx yy B08J1
xx yy B08J1
xx yy B08N1
xx yy K10-2 CLKT H
xx yy K10-2 CLKT H
xx yy K10-2 CLKT H
xx yy E08U1
xx yy E08U1
xx yy D18 - PGC 04 (1) H
xx yy D18 - PGC 04 (1) H
xx yy D18 - PGC 04 (1) H
xx yy B08H2
xx yy B08H2
xx yy B08H2
xx yy B08H2
xx yy K1-4 SERVICE H
xx yy K1-3 ISR (3+7) H None
xx yy B08S2
xx yy B08S2
xx yy B08S2
xx yy K12-3 TRAPS B02C1 - B08P2
xx yy K1-3 B DEST (0) H
xx yy K1-4 B SOURCE (1) H B09H1 - F11M2
xx yy K1-3 ISR 12 L
xx yy K1-3 ISR 7 L
xx yy K10-4 RTI H
xx yy K10-2 JSR H
xx yy D18 CLK NPR H
xx yy K10-3 RTS B09D2 - E11T2
xx yy K1-4 SERVICE L
xx yy K13-3 TIME OUT (0) H
xx yy K1-4 FETCH (0) H
xx yy K10-2 TRAP L
xx yy K13-3 -(ST+SR) H D06D2 - B11T2
xx yy B08V1
xx yy K2-3 CLR PTR L None
xx yy K2-3 PERIF REL L None
xx yy DEVICE 2+3 BG06
xx yy K1-2 R/W2 H
xx yy B08M2
F02J1 C06V1 - Unlisted (Not in original table; added by hand)
B09H1 F11M2 -