Using old Psion computers like the Series 3/3a, Siena or HC/MC etc. can be a right PITA trying to get them connected to their original (DOS or 32bit windows) connectivity software (e.g. MCLINK.EXE or PsiWin or rcom/slink etc.) – here’s why:
Back in the late 1980s and early 1990s when the Psion SIBO machines were originally designed “RS232” was king: an asynchronous physical layer serial interface definition that had evolved from the (1960s!) world of dumb terminals connected to modems or mainframe computers… The RS-232 specification has up to 11 signals (from https://en.wikipedia.org/wiki/RS-232) and in the pre-USB world that meant up to up to 11 separate wires in a cable to support the full interface.
The software that drives Psion’s proprietary link protocol used by both PsiWin & MCLINK needs all of the control signals RTS/CTS/DCD/DSR/DTR.
In 1996 USB 1.0 came along and had a go at emulating these older serial interfaces with its Communications Device Class (CDC). (Interestingly it wasn’t until USB 1.1 in 1998 that USB devices began to be widely adopted).
Certain USB-to-RS-232 adapters only provide the bare minimum of the original RS232 control/data signals (usually just Rx/Tx/GND/CTS/RTS) – these will not work with Psion’s PsinWin/MCLINK/etc.
For maximum compatibility always use USB-RS232 adapters that support RTS/CTS/DCD/DSR/DTR – These will work with PsiWin/MCLINK
I’ve had most luck with this old (early 2000s?) generic PL2303 adapter…
Room 7609 
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