Serial Port Communication on the same Windows machine not working

Question

Excuse me, quick question:

I have this hardware setup:

Same machine: \"Com3\" -> USB -> To Serial -> To USB -> \"Com4\"

Answer 1

It cannot block when there is data available. What you sent either got stuck in the transmit buffer, got lost due to a wiring mistake, triggered an error or was ignored. If it works with another program then a wiring mistake can't be the problem.

Do keep in mind that just setting the Baudrate is not enough, you must also use set the DataBits, Parity and Stopbits properties to match the device settings. A mismatch can trigger an error, the kind you can only see when you write an event handler for the ErrorReceived event. Never skip that event, confounding problems can occur if you never check.

And above all the Handshake property must be set correctly. The proper value depends on how the ports are wired together, it is too common to not connect them. Start by setting it to Handshake.None so a wrong state for the DSR and CTS signals can't block reception and a wrong state for the DTR and RTS signals can't block transmission. Beware that it is common for another program to enable hardware handshaking, a mismatch is guaranteed to cause communications to stall.

If you use synchronous reads instead of the DataReceived event then you should in general deal with the possibility that a device is not responding. Either because it is powered off, not connected at all or malfunctioning. Use the ReadTimeout property for that so your program cannot hang. Aim high, 10000 milliseconds is a reasonable choice.

Beware the randomness of this problem, putzing around with another program can easily get the port configured correctly and now it will suddenly work. And beware that starting a thread accomplishes nothing, it will now be that thread that gets stuck and the Join() call will deadlock.