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Talking to the pins

A project log for Getting online with a 1987 Psion Organiser II

Bringing an Eighties handheld classic into 2019 with a little help from a Raspberry Pi. At least, that's the idea.

James FosseyJames Fossey 06/13/2019 at 19:160 Comments

The good news: I have managed to physically connect the Pi and Psion. I have also managed to send a simple 'signal' (literally 'pulses' i.e. single bits) from the Psion to the Pi's UART RX pin using SSCR* - but not the other way round. At least, not yet.

It turns out that reading and 'toggling' the pins in the Psion top slot isn't easy! As far as I know there is no simple command in OPL (the Organiser's built-in BASIC-esque high level programming language) that will let me set/read the state of the 3 general-purpose pins in the top slot. It looks like I will need to concoct some simple (?) machine code routines to toggle and read these pins. Until then, I have to stick to Organiser Tetris for my 8-bit entertainment...


Reading data from the Pi using SSCR would only be possible if I get hold of an 'official' Psion Organiser Comms Link, or something hardware compatible with this device. The Comms Link was the commercial name of the RS232-based device Psion produced in the '80s to allow the Organiser to communicate with the PCs of the time - back when PCs had serial ports and monochrome monitors. Psion Comms Links still pop up on eBay from time to time but they aren't cheap. A modern USB version has also been produced and sells for 20 Euros plus postage.

For now, though, I'm going to try and do without a Comms Link. Let's delve into the wonderful world of 1980s machine code...

*pedantic note:  the only pin I can toggle with SSCR is pin 2 on the top slot (SD0) which is not the pin I showed in the table in my last post!

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