Scan of RogAlgol Paper

This scan is out of "DECUS EUROPE Ninth Seminar Proceedings 1973"

German OS/8 Handbook

A little OS/8 handbook from digital Germany.

MICO dual serial interface module

Configuration document for mico dual serial interface.

MICO 32K memory module

Original documentation for mico 32K x 12 MOS memory.

LogAbax LX180 printer manual

User and maintenance manual for the LogAbax LX180 printer.

ROM Images:


The ROM images I used to repair my defective vt100 as binaries and as intel .hex files.
I also put in the concatenated ROM images used to burn a 2764.


Power Control 861B

Schematic of the DEC 861B power control

Geveke ASR33

With kind permission of Getronics

Scanned schematics for the Reader Run Control Card

the Motor Control Card and a Wiring Diagram for the ASR33 with UCC6

HP ASR33 Reader Run Control Card

Reverse engineered schematic for the Reader Run Control Card of my HP ASR33 Teletype.

I could not identify D1 and T1, but they are a normal diode
(maybe 1N1048) and a pnp transistor (maybe BC237).
There is also a schematic which shows how the Reader Run
Control fits into the ASR33 (HPtty_v3.pdf (45 KB)).

RS232 to 20 mA converter

Here is the schematic of my RS232 to 20mA converter.
I will take no warranty, that it is working for you.
It just works for me (tested with two of my three ASR33s
and an old 80486 notebook).

Parallel printer interface

Reverse engineered schematic (postscript output from Eagle)
for my parallel printer interface
(manufacturer unknown - used with LogAbax LX180 matrix printer)

Plessey RK8E clone

After all I got and scanned the Plessey documentation for the RK8E clone (PM-DC/8) and a RK05 compatible disk drive (PM-DD/8).

The now obsolete reverse engineered schematics for my Plessey RK8E clone (in .pdf file format) are still available.

I used the RK8E schematics from David Gessweins site as a basic starting point.
New updated Version available.
Old version with some errors still available only contain modified pages.
So you should get the RK8E schematics first.
I discovered that this clone is nearly identical to the RK8E.
NOTE: I didn't care for analog stuff like resistor, capacitors, ...

Major differences are:

Differences and Anotations
M7104 700645 DEC 8881 replaced with 7438
380 replaced with 8640
7473 replaced with 74H76
314 and 8251 replaced with 7485 and 7442
8235 replaced with 74157
8235 replaced with 7400, 7404, 7432 and 7438
use of a delay line for 6RK2 L delay

Different chip numbering, placement and different routing

M7105 700647 8881 replaced with 7438
380 replaced with 8640
74155 replaced with 74139
8271 replaced with 74179

Different chip numbering, placement and different routing

M7106 700643 Crystal replaced with integrated oscillator
380 replaced with 96106 and DS8836N
74155 replaced with 7442

Besides the differences above even chip and pin numbering
are the same, placement nearly identical.

orientation of jumpers J1 and J2 is upside down

Tape Images:

Please read this license agreement from DEC before downloading and using the following images.

OS/8 Version 3B OS8V3B.IMG (371 KB)

OS/8 Version 3D OS8V3D.IMG (371 KB)

TD8E Simulation for tapes above:

Click on thumbnail to get a larger version of the preview.

Third Version of TD8E simulator "plugin" for
Douglas Jones's pdp8 emulator:

Precompiled versions works with gnome and cde but may not
work with kde.

Old Version of TD8E simulator "plugin" for
Douglas Jones's pdp8 emulator still available.

Here is a copy of README.td8e of the new Version 0.3:

Welcome to the TD8E plugin for Douglas W. Jones's pdp8 emulator
Version 0.3

At first please read the original README file	
from Douglas W. Jones, the README.txt and the
os8_license.txt file from DEC.

This TD8E plugin simulates up to four  TD8E simple DECtape
controllers with up to four dual TU56 DECtape units.

This simulation is NOT perfect and far away from being an
emulation. But it is complete enough to boot OS/8 from a
TD8E boot tape (tested with OS/8 V3B and V3D).

This new version supports two different file formats:
- DJG:	David Gesswein's high level format (HLS)
for using the OS/8 tape files (129 words per block)
of many internet sites.
- PxG:	My low level format (LLS) which supports additional
simulation features like formating a tape in
different formats (only OS/8 format tested yet).
With this file format the simulator should even pass
some of the diagnostic routines. (Not tested yet. :-( )

The different formats are distinguished by the presence of
a four byte header "tu56". If it is there it is a PxG or
LLS format tape. Otherwise it is asumed to be in DJG or
HLS format.

This distribution was built under RedHat Linux 7 on a 2.2.16-22
Kernel (OK it's outdated but you can recompile it yourself)
and tested under RedHat AS 2.1 with Kernel 2.4.20-20.7 too.

Hope you enjoy it.

Gerold Pauler

If you have any questions or found any bugs please mail to

Modified files of Douglas Jones's emulator are:

Makefile	TD8E added
kk8e.c		stubs for TD8E and TU56 inserted
ttyaccess.c	modified for Linux
utility.c	fixed one minor bug (corefile shrinking 1 word)
kc8e.c		fixed startup glitch

New files added are:

README.td8e	this file
td8e.boot	core image of TD8E bootstrap  (start at 0 7300)
warm		core image to warm start pdp8 (start at 0 7605)
td8e.c		the TD8E / TU56 plugin
tu56.c		the TD8E / TU56 GUI
os8.djg		OS/8 bootable tape in David Gesswein's format
os8.pxg		OS/8 bootable tape in Gerols Pauler's format
empty.djg	an empty tape in David Gesswein's format
empty.pxg	an empty tape in Gerold Pauler's format
pdp8e		compiled emulator (set up to support both formats)


What new in version 0.3?

Support for Sun Solaris 9 on Ultra Sparc added.
(compiled and tested on an dual processor E250
with Solaris 9 and GNU gcc)

Doesn't core dump anymore if DISPLAY environment
variable is not set.

What new in version 0.2?

Support of more than one TD8E / TU56.

Support of read only files.

Support of a new low level format.

Support of WTM switch and formatting capabilities.

Buffered I/O (for better performance ;-) )

Graphical user interface to
show WTM switch status
(re)set the WTM switch
show command and data register

show selected unit
show WRITE LOCK status
(re)set the WRITE LOCK switch
show mounted tapes and tape position


Little FAQ

How to start OS/8 from tape file?

Start the pdp8 emulator with the bootstrap core image.
./pdp8 td8e.boot
Change core file to something else.
This prevents bootstrap core image to be modified when
exiting the emulator.
Change device to DTA0 and insert name of bootable
TD8E image file.
Set switch register to 7300, press Addr.Load, Clear and Cont.
Wait till OS/8 prompt "." appears.

Is there an easier way to start OS/8?

Yes, start the pdp8 emulator with the warm start core image.
./pdp8 warm
Device DTA0 is already mounted with os8.pxg.
Set switch register to 7605, press Addr.Load, Clear and Cont.
Wait till OS/8 promt "." appears.
Date and some other settings are already preset.

Where to find more TD8E images?

Look at David Gessweins pdp8 homepage

Where to find more information about pdp8 emulators?

Look at Douglas Jones homepage

How to create a new tape?

Create a DJG* new "DECtape" using
dd if=/dev/zero of=newtape bs=380292 count=1

or create a PxG** style new "DECtape" using
echo tu56 | dd of=a bs=4 count=1
dd if=/dev/zero of=b bs=528896 count=1
cat a b >newtape
rm a b

Now you can use and mount this tape on the emulator.
First thing you want to do with it is to write a new
(zero) directory on it. To do this use the OS/8 CCL
command ZERO or run PIP /Z.

Now you have an empty tape ready for use under OS/8.

How to convert from DJG to PxG format?
How to convert from PxG to DJG format?

Sorry you have to use the simulator and run TDCOPY.

The simulator hangs after rewinding tapes in TDCOPY

No, the simulator does not hang. There are only
one or more tapes that couldn't be stopped in
time. So they spun after begin of tape.
You can stop TDCOPY with ^C.
And reset all tape positions by doing a reboot
from memory location 7605.
Don't forget to press the "clear" button before
you press continue. Because pressing "clear"
set tape position to defined starting point.

The simulator hangs after I tried to DIR (or any other
tape operation on) a drive with no mounted tape

As above, the simulator does not hang but sets
the sel/timing error flag. This results in the
OS/8 driver waiting forever.

You should not invoke tape operations on drives
which have no file mounted!!!

As above you can do a "warm" reboot from location

Typing ^C halts the simulator

This happens if the system tape (SYS:) is write locked.
Simply press continue on the pdp8 control panel.

While simulator is running it is not possible to set
drive to write enable.

You don't have write permission to the file mounted
on that drive. You have to unmount the file, change
the permissions and remount the file.

* DJG:	compatible with DECtape images (129 words/block)
from David Gessweins pdp8 page.
** PxG:	more like the files of the other simulator devices,
but not in conformance with Douglas Jones's DECtape
DWJ sets the mark track in the two most significant
bits of a byte. The remainig 6 bits are the corres-
ponding data bits of two line.
My format (PxG) keeps the mark track as the most
significant bit of a nibble. The three lower bits
are the corresponding data bits of this line.
Then two lines are packed into one byte.

TM:	pdp8, OS/8, DEC, DECtape, TD8E and TU56 are registered
trademarks of digital equipment corporation.