Need help to read/write uart2 on a BB-XM

it may be that the chip is quite capable of hardware flow control but the manufacturer cheaped out with the serial wiring so just didn’t bother to wire up those pins?

That’s exactly what I have in mind. There simply is no way to know from what you can read over USB.

Interesting info about controlling USBSerial dongles.
Is there anyway of testing of a new dongle – to see if the control lines work/connected?
Perhaps a rs232 plug modified with crossover pins/and a prog to test them.

Have a Windows comms prog ‘CWCom’ that reads two pins of a rs232 port
pin 6 ‘Data Set Ready’ and pin 4 ‘Data Terminal Ready’ for input from a morse key (switch) – any ideas how that works?
Is it possible to do be done with RISC OS?

Yes you should be able to do that with any of the motherboard Serial or USB serial devices.

DTR is one of only 2 pins that you can control (DTR and RTS) usually DSR at the other end of the cable is connected to DTR at the local end and DTR is used to tell the other end when it can send when using handshaking. Similarly RTS/CTS are usually connected when using RTS handshaking. So I expect you use DTR to send to the device – not sure why you would maybe to enable it – and your program would read DSR to signify a key press.

If you have it connected to Serial: OS_Args 9 (IOCtl) will read and write the pins. To test just connect DTR to DSR and changing DTR will change DSR which you can see with OS_Args

Edit: Maybe DTR is used to supply power ie you enable DTR and the key switches it to DSR and you read DSR high. It’ll switch to the ground pin for DSR low

Edit2: If it is just a switch you could do the same thing with GPIO pins if your computer has those.

Write a little program to toggle DTR and RTS every two seconds and probe the far end with a multimeter… You could then hook one by one to RTS, DCD, CTS, RI, and the other one (DTD?). Then just look at the inputs to see if they change…