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PDT-11/150

Note both the User Guide below and the Technical Reference manual are currently available at Bitsavers

User Guide EK-PT150-UG-003
This was the first PDP-11 compatible machine I owned. It is a small LSI-11 system compatible with programs developed on a PDP-11/03. One of the histories suggests it was the fore-runner of the PRO series. It had two RX01 style drives, a CPU, and a minimum of three SLU ports. This was all in a dedicated package, minimal expansion was possible as there was no backplane. The disk drives were built into the case, and used a dedicated controller board and wiring harness. According to my manual it was sold as a single or doulbe drive system, there were three RAM options (16,32,or 60kb), and the three terminal ports, J4-J6, below were optional.

View of terminal connection on back of PDT System:

                  reset                   fuse   on
                    o                             o
                  test         fan               off

     Optional
     Terminals
   -----------
   |   J6     |      J3 modem
   |   J5     |      J2 Printer                 -
   |   J4     |      J1 Console            power  -
   |__________|                                 -
The SLU connectors, J1 - J6, are DB 25 EIA connectors. All but J3 are female and support only GND (7), XMIT (2), REC (3), RDY (20). J3 is male, and additionally supports modem control signals (pins 4-6, 8,11,12,15,17,22) as well as swapping the XMIT (2) and REC (3) pins. Later on the manual implies the printer is write only (no RCSR nor RBUF).

The front pannel has 4 indicators:

  • 1 Lights to indicate a system error in self test, can also by controlled by user via a system register.
  • 2 Lights to indicate system waiting for autobaud response from console. Occurs after a reset. Note autobaud detect can be disabled by switch S1-1.
  • RUN lights to indicate LSI-11 processor is executing instructions.
  • POWER lights to indicate +5 vdc power is present.

There is a three position toggle on the back:
Reset (up) - clears registers and initializes PDT11
Normal (middle) - normal running mode
Test (down) - initiate diagnostic mode and allows BREAK detect from console

Inside the top cover there is a five position dip switch, S1,
factory configured as follows:
1   off  Console terminal autobaud enabled
2   on   line time clock interrupt enabled
3   off  dynamic RAM refresh enabled
4   on   self-test function mode switch enabled
5   off  manufacture mode disabled

The console autobaud detection was new to me. If enabled (the default) one presses the '@' key twice (you may also need to be pressing the shift key on some systems) when the 2 indicator LED is lite to start the system. This allows the system to detect the baud rate of your terminal automatically.

The USART (SLU) parameter register at 177420 controls the operating parameters for the SLU ports (J1 - J6) and the two leds (1 & 2). The base CSR and interrupt vector, vec=, for the SLUs are shown below, these assignments cannot be modified:

  • J1 console - 177560, vec=60
  • J2 printer - 177514, vec=200
  • J3 modem (asynchronous) - 176610, vec=330
  • J3 modem (synchronous) - 176620, vec=340
  • J4 Terminal - 176500, vec=300
  • J5 Terminal - 176510, vec=310
  • J6 Terminal - 176520, vec=320
All but the printer have four consecutive registers including the CSR for each of the indicated CSR above and two consecutive interrupt vector locations. The printer only has two transmit registers and a single transmit vector.

The console and line printer have a maximum baud rate of 9600, However when using special multi code key functions (as in KED's PF keys) 4800 baud is recommended for the console. The modem will operate at 2400 baud in synchronous mode and 4800 in asynchronous mode. The three cluster terminals (J4-J6) have a maximum speed of 2400 baud. There is normally a SPEED program that will configure these ports for you.

The disk drive controller uses three registers with a base CSR at 177170 and interrupt vector 264. I think it looks like an RXV11.

The line clock (LTC) uses one register at 177546 and vector 100.

The format of the USART Parameter register is shown below.  It must
be written one word at a time, once for each device to be programmed.
bit             function
15	not used
14:12   device select in order {J4,J1,J2,J3,LEDs,J5,J6}
        ie J4 = 000, J1 = 001, LEDs = 100
11:8    baud rate in order {50,75,110,134.5,150,300,600,1200,
                            1800,2000,2400,3600,4800,7200,9600}
7       Set to light LED 2 on front pannel
6       Set to light LED 1 on front pannel
5	Set for even parity (else odd if parity enabled)
4	Set to enable parity
3:2	Char length in order(5,6,7,8) ie 8 bits = 11
1	Set for maintenance mode.  Used with loop back option
0	not used

The modem SLU is compatible with a DLV11-E in asynchronous mode which is how it is enabled after a reset. As indicated above it does have a synchronous mode which apparently one activates by setting the master reset bit 8 at 176624. I've never played with this and don't have the energy to describe the register formats at the moment.

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