Having scoured the forums and net for instruction I was able to piece together enough to get this up and running.
There are several threads here already though many are so old as to not work due to changes in the Pi O/s and others have the Pi instructions but not the Psion settings or any info on cables or plugs.
I have shamelessly copied and pasted from the most useful threads for much of the content and modified or added what I found was needed.
So, here is an updated collected how-to that works...
Anyone having the mad desire to connect their 25 year old Psion5 as a terminal for their Pi...enjoy.
Psion 5 as Terminal for Pi.
Raspberry Pi and Psion (8MB) Series 5 via (DIY-Null Modem) RS232(Psion) to USB(Pi) converter.
Console on USB port.
On the Raspberry Pi. (Pi3B+ used)
edit /boot/config.txt and add this at the bottom. Then reboot.
1. Copy the file 'serial-getty@.service' from '/lib/systemd/system' to '/etc/systemd/system'
This file is a generic template for setting up a serial terminal with a log-in prompt.
2. The file must be renamed, so that it points to your serial terminal which, in this case, will be ttyUSB0. The filename becomes:
3. Edit the file ...
# Edit this line
ExecStart=-/sbin/agetty --keep-baud 115200,38400,9600 %I $TERM
# To This
ExecStart=-/sbin/agetty 9600 %I $TERM
Set this to the baud rate that you wish to use. This should be the same at the computer is using at the other end.
For the Psion things don't seem to work above 9600. Difficulty connecting or garbage characters.
4. Now, enable the service with:
'sudo systemctl enable serial-getty@ttyUSB0.service'
You should get a 'Creating sim link ....' message. The service will now start up at every boot.
You can start the service without rebooting with:
'sudo systemctl start serial-getty@ttyUSB0.service'
On the Psion 5
At the main screen, Menu – Remote link – turn off
Then go to Extras – Comms
Menu – Translate Codes – Turn off "Local Echo" Turn off "Add LF to outgoing CR"
Tap on Setup, Set Comms Port to 'Serial port 0' set Baud rate ='9600' Data Bits ='8' Stop Bits ='1' and Parity ='None'.
Then deselect all Handshaking settings and then OK to connect.
Reboot the Pi and the Pi login should appear on the Psion screen.
Wiring a PC<->Psion serial cable
This is the spec for a standard (as supplied by Psion) serial cable, including the equivalent 25-pin D pinout in case you want that instead/as well. This has RX/TX and RTS/CTS 'swapped' as both devices expect to be 'in charge'. This is what's called a 'null modem' cable.
(25-pin D) 9-pin D Signal Psion
8 1 DCD not connected
3 2 --RX--\ /--TX-- 4
2 3 --TX--/ \--RX-- 8
20 4 ----- DTR ----- 5
7 5 ----- Gnd ----- 15
6 6 ----- DSR ----- 3
4 7 -RTS--\ /--CTS- 7
5 8 -CTS--/ \--RTS- 2
22 9 ------ RI ----- 6
The Psion end plug is either unobtainium or comes as part of a rather expensive cable.
I found a suitable plug from an old Laptop Port Expansion Card such as these..
https://www.delock.de/produkte/G_61603/ ... anguage=en
https://www.ebay.com/itm/184392983116?h ... xyOalTbv5b
Mine was an RJ45 network lead so needed to be wired to a 9-pin D. Though that allowed me to create a null-modem cable rather than looking for yet another adapter.
so.... PsionMX5 > serial connection to 9 pin D female to > serial-to-USB converter (UNITEK brand works) > pi
https://www.rogerirwin.co.nz/open-sourc ... t-console/