The Comms Link duly arrived on Tuesday, and after a bit of fussing around with serial connectors I have managed to get the Pi and Psion physically connected. Better still, they are actually talking properly to each other at a not-exactly-zippy 1200 baud, using the terminal emulator included with the COMMS software (see previous log). In other words, the Organiser is now acting as a 'dumb' terminal for the Pi. Trouble is, it's not exactly portable at the moment...

In this picture you can see the Organiser with Comms Link attached (bottom right) and the hefty Comms Link cable, which terminates with a female DB25 connector on the left of the photo. My Raspberry Pi 3 (top right) has an RS232/TTL converter attached. The female DB9 connector on this converter is connected to the DB25 connector of the Comms Link by three red wires poked into the relevant holes. This bit is, unsurprisingly, rather fragile. See the table at the bottom.

What can I do so far? I can login to the Pi using the Organiser's keyboard and do all the basic terminal stuff. The only awkward quirk so far (other than the Organiser's tiny 16x2 screen, of course) is that the Psion's EXE key does not act like ENTER. Instead I keep having to press Ctrl-J on the Psion. The left arrow key takes on the role of Control in the Psion COMMS software.

Table of connections...