Very good question!
The serial port on other FP controllers where RS-485, is this different on the FP-2000?
I have not had an opertunity to write an app that uses the serial port on a FP-2000 yet and will monitor this question for insite on how to do this. (in fact last night I was wondering if I can still daisy chain devices off the serial port of the FP-2000 like I could do the older ones. This thought then lead me to wonder if I could control this port being used for other FP units or use it to do custom interfaces.)
I can tell you this though. Most of the serial printers that I have seen signal these conditions by ether de-asseting a handshake line (if used) or by sending an Xoff. This is dependent on the printer.
That's all I can offer for now,
Ben