Computer Museum - Replacement DEC KM11

How to build a clone of the DEC KM11 maintenance module (by Tony Duell)

The KM11 is the maintenance module for the PDP11/05,10,40,45 CPUs, RK11-C, RK11-D controllers, RX01 floppy drive, and probably many other devices. It is not commonly available second hand, so if you want one, you will probably have to build it yourself. Here I'll describe how I did just that.

Components :

5* 1k Resistor
28 * 330R resistor
28 * red LED
1 * 330uF Capacitor
1 * 7400
1 * 7406
4 * ULN2803
3 * SPDT (single pole change over, form C) toggle switch
1 * SPDT biased toggle switch
Prototyping board/PCB (your choice)
1 * DEC M957 cable connector module - this is the single-height connector module that was supplied with the DR11-B parallel port. If you can't get this, you can use anything else that will fit in a single-height slot, and will make a separate connection to each of the 36 pins. Ideas include etching one from PCB, cutting down another DEC board, cutting down an S100 prototype board, etc.
1 * Box (if you decide to make it a separate module linked to the M957 by a cable, as I did. A box with a clear lid avoids having to drill holes for the LEDs)
Cable, wire, solder, etc.

I'll present this as a set of instructions and part circuit-diagrams. I'll not show the power connections on the IC's - all the pins indicated as ground (pin 7 on the 7400 and 7406, pin 9 on the ULN2803) are linked to ground, Vcc on the TTL chips (pin 14 on the 7400 and 7406) are linked to +5v. The protection pin (pin 10) on the ULN2803 is linked to +8V. I'll also assume you have the pin-outs of the chips, and so I'll not be numbering all the pins Also, note that I use the DEC labeling of pins on the M957 board. Looking into the slot socket, they are layed out as :

Solder side Component side

A2 A1

B2 B1

C2 C1

D2 D1

E2 E1

F2 F1

H2 H1

J2 J1

K2 K1

L2 L1

M2 M1

N2 N1

P2 P1

R2 R1

S2 S1

T2 T1

U2 U1

V2 V1

Right, down to construction :

Power wiring

The power voltages are obtained from the slot as follows

(B1)-----------+----  +8v
               | +
              --- 
              --- 330uF
               |
               |
              ---
              ///

(A2)----------------+5v

(C2)--+
      |
(T1)--+
      |
     ---
     ///

Switches

There are 4 switches, all of them slightly different!. I mounted them on the front of the box in which I mounted the prototyping board containing the driver chips an LEDs. S1 was on the left, and S4 (the spring-biased one) was on the right. Wire them up as follows :

         /o
        /
 +-----/  o------(B2)
 |     s1
---
///


             +5v
             ---
              |
              /
              \ 1k
              /
        /o    \
       /      |
 +----/  o----+-----(V2)
 |     s2
---
///

      +5v
      ---
       |
       /
       \ 1k
       /      
       |       '00
     +-+------|\             |\
     |        | )o---+-------| |>o-------(A1)
     |     +--|/     |       |/
  S3 o     |         |       '06
  +\       +-------+ |
  | \o   +---------)-+
  |  |   +----|\   |
  |  |        | )o-+
  |  +--------|/
 --- |        '00
 /// |
     |
     / 1k
     \    +5v
     /    ---
     |     |
     +-----+


      +5v
      ---
       |
       /
       \ 1k
       /      
       |       '00
     +-+------|\       
     |        | )o---+-------(U1)
     |     +--|/     |
  S4 o     |         |
  +\       +-------+ |
  | \o   +---------)-+
  |  |   +----|\   |
  |  |        | )o-+
  |  +--------|/
 --- |        '00
 /// |
     |
     / 1k
     \    +5v
     /    ---
     |     |
     +-----+

(S4 is spring-biased to the position shown). So, to recap. S1 grounds pin B2. S2 grounds pin V2, which is pulled up by a 1k resistor. S3 is debounced, open-collector buffered, and then drives pin A1. S4 is debounced, and then drives pin J1. All these pins should be high/floating with the switches in the 'off' position.

LED's
Mount 28 LED's in a 7 * 4 matrix either on the box lid, or on the circuit board if the lid is transparent. Each LED is driven by one section of a ULN2803 chip - like this :
```
 
                          +8v
                          ---  
                           |
                           |
                          ---
                          \ /  \  RED LED 
                          ---   \
          |\               |     V
(pin)-----| |>o----/\/\/---+
          |/
        ULN2803 (1 section of 8).
```
Do not try to replace the ULN2803 device with a TTL driver. DEC put 1k resistors in series with some of the signals, and a TTL buffer will not be driven correctly
As I said, the LED's are mounted in a 7 column,4 row matrix. Link the inputs to the driver chips to the pins as shown in the diagram below : K2 J1 P1 R1 S1 N2 R2 N1 C1 L1 K1 M2 D2 E2 V1 T2 F1 S2 F2 H2 H1 P2 U2 D1 M1 E1 J2 L2

Finally
The meanings of the LED's and switches are shown in the DEC maintenance manual or Engineering drawings for the particular device.

Solder side	Component side
A2	A1
B2	B1
C2	C1
D2	D1
E2	E1
F2	F1
H2	H1
J2	J1
K2	K1
L2	L1
M2	M1
N2	N1
P2	P1
R2	R1
S2	S1
T2	T1
U2	U1
V2	V1