Thanks Marcus,
I was thinking of you when I wrote this up. Your projects seem to revolve around connecting very unusually things to the PLCs.
One thing I forgot to mention, is that the cheap TTL to RS232 level converter that I used does not drive any of the handshake lines (DSR ...). The TRi PLCs usually drive a single pin at about +9V and this signal is usually DSR, data set ready. TRi PLCs don't pay any attention to the handshake signals from the other device nor does the PLC ever de-assert the handshake signal that it does provide.
This may have some effect on cabling. Some external devices need to see an asserted signal before these devices are happy. If your cabling used the signal on the PLC end of the serial cable to drive the handshake signal on other end of the cable, you may need to adjust your cabling.
There are many of these TTL to RS232 level converters on the market. Many of them have jumpers that would provide greater flexibility.
The level converter that I used has no jumpers. The standard TTL / rs232 converter chip used on the board, does have an unused RS232 driver that could probably be used to drive a handshake line.
Best regards,
Gary d