KA11 changes for the KT11-B
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".
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 |
| D-BS-7605961-0-9 | 1 | KA11 to KT11 Interface |
| D-AP-7605961-0-10 | 1 | PC Board Modifications |
| D-WS-7605961-0-11 | 1 | KA11 Mods for use with KT11-B |
KA/KT Interface
The KA11 and KT11-B are connected by a UNIBUS between them (which carries all the CPU's normal bus functions, such as memory cycles), and also by an additional cable. That cable carries various other signals, mostly internal signals of the KA11 which are used by the KT11-B (along with a few additional ones which are synthesized specially), although there are also a few signals from the KT11-B, used in the modified KA11.
On the KT11 end, the cable 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 | - | Unused |
| B1 | KA11 | Odd address error | B2 | - | Unused |
| C1 | - | Ground | C2 | - | Ground |
| D1 | KT11 | PGC 04 | D2 | KA11 | RTS |
| E1 | KA11 | DEST | E2 | KA11 | CLKT |
| F1 | - | Ground | F2 | - | Ground |
| H1 | KA11 | SOURCE | H2 | KA11 | -TRAPS |
| J1 | KA11 | ISR 12 | J2 | - | Ground |
| K1 | - | Ground | K2 | KA11 | SERVICE |
| L1 | KA11 | ISR 7 | L2 | - | Ground |
| M1 | KA11 | -RTI | M2 | KA11 | TIME OUT |
| N1 | - | Ground | N2 | - | Ground |
| P1 | KA11 | JSR | P2 | KA11 | FETCH |
| R1 | - | Ground | R2 | - | Ground |
| S1 | KT11 | CLK NPR | S2 | KA11 | TRAP |
| T1 | - | Ground | T2 | KA11 | [ST+SR] K13-3 |
| U1 | - | Unused | U2 | - | Ground |
| V1 | - | Unused | 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 changes
The changes to the KA11 include a small number of modifications to several boards in the KA11 (below), and a number of changes to the wiring of the CPU backplane (also below).
An M138 FLIP CHIP (octal three-input NAND gates) is plugged into the KA11 backplane (in slot B08, otherwise unused), to provide additional gates, which are used to synthesize some of the signals sent across the KA11 - KT11-B interface cable. (Recall that slot B09 is where the interface cable between the KT11-B and KA11 plugs into the KA11.)
Board modifications
Alas, there is only one known set of the prints of the KT11-B changes to the KA11 - and that set is missing the page: "PC Board Modifications", D-AP-7605961-0-10. Luckily, there is apparently just enough duplicate information elsewhere (including a hand-modified set of KA11 prints, showing the changes to support the KT11-B) to allow it to be re-created.
The following are the changes on the three KA11 boards which are modified (KA11 backplane wiring changes are given in other sections below):
On the M824 Priority card, page K3-2:
- The NAND gate (E24) feeding, via another NAND gate (also E24) the NPRF flop (E14) is re-purposed (as a NOR with inverting inputs):
- Although one input (pin 5) remains connected to pin D12S1, that pin is now connected to K2-3 PERIF REL L
- The other input (pin 4) is connected to the output of the NOR gate at the top of the page (E18, pin 1)
- The output (pin 6) is used as an input to the next gate
- A NOR gate is added between that gate, and the clear input of the NPRF flop; the 'KA11 mods' print set shows one gate used for this (E25, a 7402), but the hand-written mods to the standard KA11 prints show a different one (E10, a 7450)
- In both prints, one input is connected to the output of the previous NAND gate
- In the 'KA11 mods' print set, the other input is also connected to that signal; in the hand-modified set, that second input is connected to the '1' output of the NPRF flop (E14, pin 5)
- The output is connected to the clear input of the NPRF flop (E14, pin 1)
- The input of the NAND gate (E24, pin 2) which was being driven by the re-purposed NAND gate is now driven by the same signal as the other input (pin 1)
On the M822 Flag Control card, page K12-2:
- The line in the upper right-hand corner between the output of the NAND gate (E28) and the preset input of the OVFLF flop (E15, pin 1) is deleted
On the M724 Bus & Console Control card, page K13-2:
- The line from the E50 9601 timer low output (pin 6) to the clock input (pin 11) of the E46 Time-out flop is cut
- A spare 7400 NAND gate (in E26), used as an OR with inverting inputs, has its output (pin 8) connected to the flop's clock input; its inputs are:
- One input (pin 10) is connected to the timer high output (pin 8)
- The other input (pin 9) is connected to backplane pin F06C1 ('FORCED TIMEOUT')
Wires removed
The following lists of wiring changes on the KA11 backplane give the content 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). The goal is to eventually cross-check all this information with the prints, to verify all data, and supply that which is currently missing here. '?' indicates a currently un-readable character.
| 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. Text in italics are comments added during the transcription to this page.
| From | To | Signal | Comment |
|---|---|---|---|
| E03F1 | F06H1 | K1-2 SCLK L | |
| D?2C2 | D12T1 | GND 12 | None |
| D11B1 | D02N1 | K10-3 ODD ADDRS ERR L | None |
| F04P2 | B08A1 | K10-2 ODD ADDRS ERR L | |
| F04P2 | B08B1 | K10-2 ODD ADDRS ERR L | |
| F04P2 | B08C1 | K10-2 ODD ADDRS ERR L | |
| B08D1 | B08E1 | B08D1 | |
| B08D1 | B08L1 | B08D1 | |
| E03F1 | B08M1 | K1-2 SCLK L | E04L1 - B08M1 |
| B08J1 | B08K1 | B08J1 | |
| B08J1 | C06J1 | B08J1 | |
| B08N1 | B09B1 | B08N1 | |
| E04K1 | B08P1 | K10-2 CLKT H | |
| E04K1 | B08R1 | K10-2 CLKT H | |
| E04K1 | B08S1 | K10-2 CLKT H | |
| B08U1 | B08D2 | B08U1 | |
| B08U1 | B08F2 | B08U1 | |
| B09D1 | B08F1 | D18 - PGC 04 (1) H | |
| B09D1 | B08H1 | D18 - PGC 04 (1) H | |
| B09D1 | B08F2 | D18 - PGC 04 (1) H | |
| B08H2 | B08J2 | B08H2 | |
| B08H2 | B0K2 | B08H2 | (Presumably 'B0K2' is a typo for 'B08K2') |
| B08H2 | B08L2 | B08H2 | |
| B08H2 | E07P2 | B08H2 | |
| D03T2 | B08R2 | K1-4 SERVICE H | |
| E03L2 | B08N2 | K1-3 ISR (3+7) H | None |
| B08S2 | B08T2 | B08S2 | |
| B08S2 | B08U2 | B08S2 | |
| B08S2 | B08V2 | B08S2 | |
| D11B2 | B08P2 | K12-3 TRAPS | B02C1 - B08P2 |
| F03J1 | B09E1 | K1-3 B DEST (0) H | |
| F03M2 | B09M2 | K1-4 B SOURCE (1) H | B09H1 - F11M2 |
| E03R1 | B09J1 | K1-3 ISR 12 L | |
| E03K1 | B09L1 | K1-3 ISR 7 L | |
| F04S2 | B09M1 | K10-4 RTI H | |
| C04D1 | B09P1 | K10-2 JSR H | |
| B09S1 | F02U2 | D18 CLK NPR H | |
| E04R1 | B09D2 | K10-3 RTS | B09D2 - E11T2 |
| D03P2 | B09K2 | K1-4 SERVICE L | |
| F06M1 | B09M2 | K13-3 TIME OUT (0) H | |
| F03J2 | B09P2 | K1-4 FETCH (0) H | |
| C04P1 | B09S2 | K10-2 TRAP L | |
| C06V1 | B09T2 | K13-3 -(ST+SR) H | D06D2 - B11T2 |
| B09V2 | F06C1 | D18 FORCE TIMEOUT H | |
| B08V1 | B09H2 | B08V1 | |
| F02J1 | D06D2 | K2-3 CLR PTR L | None |
| F02P1 | D12S1 | K2-3 PERIF REL L | None |
| B12P2 | B12V2 | DEVICE 2+3 BG06 | |
| D11H2 | E04L1 | K1-2 R/W2 H | |
| B08M2 | B09E2 | B08M2 | |
| F02J1 | C06V1 | K2-3 CLR PTR L | Unlisted (Not in original table; added by hand) |
| B09H1 | F11M2 | K1-3 ISR 12 L |
