digital equipment corporation · maynard, massachusetts
This interface allows control of my PDP-8/E system.

This site is primarily run off of a 486 PC  running the Apache web server under Linux. The control of the system is done with a special board I created which is connected to the parallel port on the 486.  The 486 also has a 4 port serial card connected to the console serial cards in the PDP-8.  This machine is also our internet gateway and print server.  The web camera is connected to an AMD K6-350 computer also running Linux (most of the time).

The power to the equipment is controlled by a card connected to the parallel port which controls the power controllers in the racks.  It also has a master shutdown connected to a smoke detector, over voltage detector, (in future) temperature sensor.  It also will turn off power until I push a reset if power drops out.  Currently I use it also to sequence power to the RK05 drives so they go to load modebefore power is removed.   The PDP/8 system takes over 15 amps when the computer and all the peripherals are on.  I was tripping the breaker until I split them across two circuits.

The front panel control is done with a special interface board I created which is connected to the parallel port on a 486 computer .  The front panel Java program is based on the code from Douglas Jones's emulator.  Connecting to the actual front panel would have required non-reversible modification to the board that I didn't want to do.  I used the schematics for the later PDP-8/M style interface board for the implementation and it should act very similar to operating the actual front panel.  Since the rotary switch on the real front panel is always set to state it will only show the same light pattern as on the second row of the Java version when it is set to state.   The web view of the panel shows more flicker than is actually visible.  The computer is a PDP-8/E which originally had white incandescent bulbs but almost all were replaced before I got the machine with red LED's.  With the web camera I have they were not visible so I have put the front panel board from the PDP-8/M in which has brighter LED's.  These LED's are original. This interface board also supports databreak (DMA) transfers between the PC and the PDP-8. This is used to quickly transfer data to the PDP-8.

The storage devices available are two RK05 hard drives, a dual RX02 8 inch floppy drive in RX01 mode, and a dual TU56 DECtape drive.  I have left their control switches set for normal operation since remote control of them is not currently possible.  Since robot arms are a little out of my league, to change the media in the drives I transfer new contents from the PC.  That is done by reading out the current memory, loading a transfer program and then using that to transfer the contents to the PC via the databreak.  The memory contents are then put back and execution resumed.  Since it is difficult to find all processor state to save, this may not be transparent to all programs running on the PDP-8.  Data errors on the interface between the PDP-8 and PC are detected but a re-read test is not done on transfers to the PDP-8.  The RK05 is very reliable, I think the RX02 is but the TU56 has read errors sometimes.  I may add a verify later.

The RK05 drives actually being used is the one in the tall PDP-8/E rack shown in the webcam or the home page picture.   and the lower one in the short rack (drive 2).  The drive above has a bad bearing in the head positioner which I haven't had time to try to fix.  The RX02 being used is the lower one in the small table under the VT78 on the right in the picture.  The TU56 is above the PDP-8/E which is also in the tall PDP-8/E rack.

The web camera is an old Sony 8 handycam connected to a Hauppauge video capture card.  The BTTV  (patched) software is used to talk to the video capture card and the University of ULM webvideo software generates a streaming GIF where it only updates the part of the picture that changed.  I will probably be switching to a Java based web camera since this software is no longer being maintained for Linux and Java appears to be adding support for video.  The camera doesn't have quite enough low light sensitivity to pick up the lights well on the computers.  Long term I was planning to allow control of the zoom lens and pan and tilt so you could select what you wanted to look at.  I will also see if I can get a better camera (any donations?).

The first PDP-8 I got was the (rackless) PDP-8/I now in the Data General rack.  I also got a bunch of documentation and paper tapes.  I picked that up 12 or so years ago from Washington University where I went to college.  I later picked up the Educomp rack with the two RK05's and PDP-8/M and VT78  & VT52 from Kent School for a small donation along with more documentation.  I picked up the RX02, RK05, TU56, VR14, various cards and much documentation from Temple University.  The other PDP-8/I I picked up a few years ago when somebody posted to alt.sys.pdp8 saying they had to get rid of one.  I have picked up various documentation and boards from various other people. Thanks to all who have made donations and swapped stuff.

The Kent School computers were used in the business office to do the school administration from at least 1982 to 1986.  The Washington University machine I don't have much information on but appears to have been connected to a Diffractometer.

Feel free to contact me, David Gesswein djg@pdp8online.com with any questions, comments on the web site, or you want to donate equipment, documentation, software etc to this project.  I am interested in anything PDP-8 related, computers, peripherals used with them, DEC or third party, or documentation.  I will pay shipping and handling.