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 :

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 sideComponent side
A2A1
B2B1
C2C1
D2D1
E2E1
F2F1
H2H1
J2J1
K2K1
L2L1
M2M1
N2N1
P2P1
R2R1
S2S1
T2T1
U2U1
V2V1

Right, down to construction :

  1. Power wiring

    The power voltages are obtained from the slot as follows

    (B1)-----------+----  +8v
                   | +
                  --- 
                  --- 330uF
                   |
                   |
                  ---
                  ///
    
    (A2)----------------+5v
    
    (C2)--+
          |
    (T1)--+
          |
         ---
         ///
    
  2. 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.
  3. 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

  4. Finally

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