PDP-11 SPACEWAR running again!

Mattis Lind mattislind at gmail.com
Mon May 10 13:26:44 CDT 2021

Today I finally got the SPACEWAR version for PDP-11/10 running again on my
PDP-11/05 with AR11 board. I played a couple of rounds together with my
daughter. She was better than me. Quite hard game IMHO.


Bill Seiler and Larry Bryant wrote this version in 1974 and submitted it to
DECUS. It was believed to have been lost to history. But Bill had saved the
printouts from the PAL11 assembler. He sent me scans of these printouts as
pdf files. I then transcribed it into source files and iterated several
times in SimH to get a clean build and link. I got some help from people
here doing OCR on some files. But the lines mostly confused the OCR process
so a lot of errors was introduced. It turned out that it was easier to just
transcribe the whole lot by hand than finding and correcting errors.

The AR11 is somewhat different to the AD01 and AA11 that Bill and Larry
used. AA11 has a 12 bit 2’s complement D/A while the AR11 is only 10 bits
and not 2’s complement. I did some patches and eventually got everything

I also connected a couple of analogue joysticks. The fire button is just
short ciruiting the viper of the potentiometer to the 5V supply lead. The
screen is a HP1332A vector screen.

All the transcribed code, AR11 patches and build instructions are available
on github. https://github.com/MattisLind/SPACEWAR

It should be possible to adapt it to orher types of A/D and D/A hardware if
anyone wishes to do so. However the gameplay might be harder when running
on a faster PDP-11?

Have fun!


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