• Please review our updated Terms and Rules here

IBM I/O Selectric terminal interface for a microcomputer, circa 1980


Veteran Member
Apr 26, 2011
Brisbane, Australia
Back in the late 70s early 80s Dad brought home an IBM I/O Selectric terminal - probably a 2741 or MT/ST I/O Writer, I don't recall - that we planned to use as the terminal for our Fairchild/Mostek F8 development kit board that Dad imported from the USA in 1978. A few of dad's IBM colleagues were also 'into' the F8 and, being the old-school engineers they were, came up with this circuit design.

Sadly we didn't build it, so I can't tell you if it works. At the time we kids were more interested in having a real VDU display screen as I/O rather than a clunky printer terminal (after all, how can you play shoot-em-up style games on a printer!). We lost interest and not long after bought and built an Applied Technology S-100 system with a video card and it even had a programmable character generator to do basic graphics.

Our I/O Selectric languished in the cupboard for many many years after that. My parents moved a few times and interstate and the unit went missing. After a lot of searching I finally found just one bit of it - the platen, with the terminal-style large disc knobs on the ends which differentiated it from a standard IBM Selctric typewriter platen. Sadly the rest of the machine appears to have been junked and Dad must have just kept the platen for rolling out photographic prints I think, as that was his main hobby.

I decided that this circuit ought to be scanned and made available to anyone interested in seeing how it was done in TTL and discrete components. Of course these days whippersnappers would use an Arduino or RasPi to drive some MOSFETs which trip the solenoids and do all the timing and encoding in software, but I hope you find it interesting nonetheless.

You can find it as an 8-page PDF at http://web.aanet.com.au/~malikoff/misc/IBM_IO_Selectric_interface.pdf