Christian's PDP11/34 Page

• hauled it up four flights of stairs to my appartement with a friend,
• restored its power supply and a DRAM module,
• ran DEC Paper Tape BASIC,
• ran some cross-assembled bare-metal code,
• booted RT-11 via TU58 emulation,
• booted Mini-Unix with a customized TU58-emulation-like driver,
• and hauled it down four flights of stairs and up some more while moving,
• ... what's next?

Restoration

Original card layout as documented before taking all the cards out to clean (and remove some spider husks in the process):

The layout was as follows:

The DEC power supply consists of an AC input box, a frighteningly big (and heavy) transformer stepping 230V to 24V AC, and individual PSU modules for the actual operating voltages.

                                                                                  (24 V AC)
                                                                                      ,------> [H7441 5V/32A  PSU]  ----> Backplane 1
                                                                                      |
                                                                                      +------> [H7441 5V/32A  PSU]  ----> Backplane 2
                                                                                      |
    Line Voltage (230 V AC) ---> [AC Input Box] --(230 V AC)---> [Big Transformer] ---+------> [H745 -15V/10A PSU] ----> Both Backplanes
                                      ^     |
                                      |     '-------------------------------------(15 V DC)----------------------------> Both Backplanes
                                      |
                            [Front Panel Switch]
                              [Remote Switch]

This picture shows the entire Power Supply box:

The PSU is actively cooled by two 115 V AC fans pulling air through it. They are very loud.

As the PSU modules run off of 24 V AC, they can conveniently be tested using a more handy (and low-power) 24 V AC transformer.

Checking the 5V output voltage after replacing some capacitors:

The PSU should only be tested with a (minimal) load, which is what the two parallel 10 Ohms power resistors are doing here.

Turning on the huge PSU box the first time was a bit frightening, but nothing exploded or caught fire ;-)

I was greeted by the wonderful hex programmer's console, from which you can enter code (e.g. bootstrap to boot off some hardware) or jump to some code in the monitor ROM.

Some useful sites were

• Repairing the PDP-11/10 Power Supply
• PDP-11/10 Processor Restauration Project
• Field Manual Print Sets (FMPS) from Bitsavers

Card Gallery

M8266 CPU Control	M8265 CPU Datapath
M7859 Console Controller Board	Intel 8008 Powered :-)
M7891 RAM Board. 128 whole Kilobytes!	M7856 SLU/RTC: Serial Interface (Not even a full "UART"... it has a fixed Baud rate adjusted by DIP switches) and AC line frequency interrupt

Running RT11

RT11 is an operating system for the PDP11 by DEC.

You can boot it using a variety of devices. I opted for using one of the M7856 (SLU/RTC) boards as a console (required by the monitor ROM) and another one to emulate a connection to an emulated TU58 tape drive.

TU58FS conveniently emulates much of the hassle on a second computer with a serial port. It even contains a bootstrap loader for the TU58 which it can toggle into the console.

Using a C64 as a serial terminal :-)	Assembling some programs, mistyping some commands
	Calculating a Mandelbrot fractal

Running Mini-UNIX

My goal for the PDP11 was to ultimately run UNIX.

Up until now, I managed to run Mini-UNIX (see here)

As I do not have a supported disk system/emulator, i needed to write my own driver for a TU58-like device, and a PC-side emulator.

The TU-like driver is compiled/assembled by booting the original UNIX in SIMH, then building it using the ancient cc C compiler and as assembler provided.

In the end, it managed to boot Mini-UNIX veeeery sloooowly...

Zoom of the picture on the left: Showing the output of $ ls and an $ echo command running on UNIX.

Fun with the General Device Interface

Finally, some fun with the M7860 General Device Interface.

In essence, this is just a 16-bit GPIO port, just as any of today's microcontrollers would provide.

By using timing loops, a pin can be toggled to produce noise if a speaker is attached to it.

This is what is done here:

What's next?

Hmmm... Maybe something like this for emulating a hard disk?

Maybe interfacing some FPGA-related stuff?

We'll see...

Useful Links

• Gunkies Wiki
• PDP11 NL
• Bitsavers.org
• SIMH
• Retrocmp.com
• Joerg Hoppe's Github