[Mike Betts]

In your code example, you are hanging because the queue is full. It will not empty unless there is communications established.

Level shifting: TTL is a 0V to 5V signal. RS232 is usually -12V to +12V. You can not just wire the two together without some sort of level shifter (see Fowlerm's post).

Printf: Indeed, printf statements output a string (the f in printf stands for formatted). I would avoid sending binary (unformatted) data until you have your system well established and debugged. Without a serial protocol analyzer, debugging unformatted communications is very difficult.

JMHO

Mike