my PDP-11/05 system

This page shows the PDP-11/05 system I have at home.
DIGITAL introduced the PDP-11/05 and the PDP-11/10 as the first "inexpensive" PDP-11 in 1972.
My PDP-11/05 is housed in one H960 industrial 19" cabinet (from DIGITAL).
The cabinet also contains all the peripheral devices.
The following devices are in the rack (from top to bottom):

The PDP-11/05 is the OEM version of the PDP-11/10.
Hardware-wise the central processors are identical.
Both machines offer features not available on the earlier PDP-11/20, such as 4-level priority interrupt and multiple accumulators.
(The PDP-11/20 was the first 16-bit processor, April 1970).

Jumps within this page are the following:


Gé van der Veldt donated this PDP-11/05. He bought the 11/05 processor for 750 guilders from a dump store in "Oude Pekela" (a city in the northern part of the Netherlands) in 1986.
The history of the processor before that date is not known. Gé added the Perkin-Elmer and the RK05 at a later time.

When Gé wanted to expand the system, DD11-CK backplanes were scarce.
To solve that problem he changed the wire wrap on the DD11-Bx backplane that was installed in the machine to the modified Unibus structure for the slots 2 and 3, rows A and B. He did this with a wire wrap hand tool. That is how he got the "DD11-CK".

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The front panel of the PDP-11/05 has a few more buttons, switches and lights than the average Personal Computer, as you can see.
I guess this "personality" is what makes these old systems 'beautiful' when compared to a modern PC.

The console has 16 LEDs for display of an address or the data contained in an address. One LED indicates if the processor runs.
The meaning of all these lights is explained a bit further.
From left to right there are 16 switches to set up an address or to load data. The up position represents a logical 1, and the down position corresponds to a logical 0. The ADDRESS/DATA switches are often referred to as the "Switch Register", SWR.
The following 3 buttons (momentary push down) for LOADing and EXAMining an address and to CONTinue the CPU, a switch to ENABLE/HALT the CPU, one button (momentary push down) to START the processor and one button (momentary push up) to DEPosit data into a memory location.
At the right hand side is the key switch to turn off / on the system and to lock-out the switches and buttons on the panel while the system runs.

Control over the system via the console

KY11-J programmer's console indicators
    16 LEDs    The 16 LEDs either represent a 16-bit address the contents of a processor register or a memory location.
Note that the state of the ADDRESS/DATA LEDs is defined only when the RUN LED is not illuminated.
RUNThe RUN LED, when lit, indicates that a program is being executed.

PDP-11/05 console controls

KY11-J programmer's console switches and buttons
The 16 ADDRESS/DATA switches set a 16-bit address to be loaded or the 16-bit data to be stored in a processor register or a memory location.
These 16 switches are called the Switch Register, and can also be read from a program that is running.
LOAD ADRSDepressing the LOAD ADRS button down, when the computer is halted, causes the contents of the Switch Register to be stored in a temporary register within the computer. This data is also displayed in the ADDRESS/DATA lights for verification. The load address operation performs the following functions.
  • Select an address for a subsequent examine operation.
  • Selects an address for a subsequent deposit operation.
  • Selects the starting address of a program.
EXAMThe EXAM button permits the display of the contents of a selected address in the ADDRESS/DATA lights. Select the appropriate address in the Switch Register and depress the LOAD ADRS button. The depress and release the EXAM button. The contents of the selected address is shown. Several features are built into the examine function to aid in the programming of the computer.
  • While the EXAM button is depressed, the address to be examined is displayed. The data itself is displayed when the button is released.
  • If the EXAM button is repeatedly depressed, the Unibus address is incremented by 2 each time. This allows the examination of a list of addresses without repeated LOAD ADRS operations. Note that the increment is one when the general processor registers are examined.
  • If an attempt is made to a non-existent memory location, it is necessary to perform the initialize operation.
  • Only full words are displayed in the ADDRESS/DATA lights; thus bit 0, the byte address bit, is ignored when using the EXAM button with the following exception. Note that the general registers are located on byte addresses. Therefore, when examining the general registers, address bit 0 is recognized and the increment feature is modified so that sequential registers may be examined by repeated use of the EXAM button.
  • The EXAM button has no effect while the computer is in the RUN state, or when the key operated power switch is in the LOCK PANEL position.
CONTThe CONT button is used to continue a program without altering the program counter, R7, or the machine state. To continue a halted program, depress and release the CONT button. The program is resumed when the CONT button is released.
The CONT button is used with the ENABLE/HALT switch to step through programs one instruction at a time. If the CONT button is actuated while the ENABLE/HALT switch is in the HALT position, a single instruction will be executed. Interrupts are serviced in single instruction mode. In single step mode, the address of the next instruction to be executed is displayed in the ADDRESS/DATA lights.
ENABLE/HALTPlace the ENABLE/HALT switch in the HALT position; the computer will halt at the end of the current instruction providing the key switch is not in the PANEL LOCK position. All interrupts and traps will be excuted prior to halting.
This switch may be used in conjuction with the CONT button to step through programs. With the ENABLE/HALT switch in the ENABLE position, programs may be executed, once started by actuating the START button, actuating the CONT button, and the auto-restart power-up sequence.
STARTTo start a program fron the console do the following steps.
  1. Set the starting address of the program in the Switch Register.
  2. Depress the LOAD ADRS button.
  3. Position the ENABLE/HALT switch in the ENABLE position.
  4. Depress and release the START button.
When the START button is depressed, the following action occur.
  • An initialize signal is generated on the Unibus. This initialize signal resets all peripherals.
  • The porcessor status word is set to zero.
  • The program counter, R7, is loaded with the last address loaded with the LOAD ADRS switches.
When the START button is released, program excution begins with the instruction contained in the location specified by R7 and the RUN light is turned on. If the ENABLE/HALT switch is in the HALT position, the computer remains in the HALT state following the release of the START button.
Take not of the following precautions when using the START button.
  1. If the key switch is not in the PANEL LOCK position, depressing the START button while a program is running initializes the computer system and restarts the program.
  2. It is good practice to precede every program start with a load address operation.
  3. A program should not be started at an odd address or the first fetch operation will be aborted and an odd address trap will be attempted. If the stack pointer, R6, is not properly set up, the program in memory may be destroyed.
DEPThe physical operation of the DEPOSIT button requires it to be lifted for actuation. The DEP button allows the contents of the Switch Register to be deposited in a Unibus address, which is typically specified by a previous load address operation. To deposit the "BRANCH SELF" instruction (777 octal) in location 200 octal, first set the Switch Register to 000200, and then actuate the LOAD ADRS button. Set the Switch Register to 000777 the lift and release the DEP button.
Several additional features are built into the deposit function.
  • While the DEP button is actuated, the address to be effected is displayed in the ADDRESS/DATA lights. The data itself is deposited and displayed for verification when the button is released.
  • If the DEP button is repeatedly depressed, the Unibus address is incremented by 2 each time. This allows the deposit of an entire program with only one LOAD ADRS operation.
  • If an attempt is made to deposit into a non-existent memory location, it is necessary to perform the initialize operation.
  • All deposit operations affect full 16-bit words. Bit 0, the byte address bit, of the address is used only when depositing into the general registers; otherwise, bit 0 of the address is ignored.

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THIS   11/05  SYSTEM   CONFIGURATION PDP-11/05 in BA11-K box

As usual, slot #1 is at the right hand side when you stand in front of the computer. So, from right to left you see the following system units (SU) in my PDP-11/05.

  1. KD11-B PDP-11/05 processor 9-slot system unit
  2. DD11-CK Unibus expansion 4-slot system unit
  3. K11-D RK05 interface 4-slot system unit
  4. DD11-CK Unibus expansion 4-slot system unit

>   All the system units are connected with a M9202 module.

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