Robert Newson wrote: ...
Hardware handshaking is [almost] vital to ensure correct input of serial data - especially if both ports are being used. The way it is done is that the 8749 asserts the ready for input line (Ser1.CTS & Ser2.DTR - of the port on which it is expecting data) for a short time and then clears it. If both serial ports are open, it then asserts the other one. This flip-flop nature of the control line(s) can be observed by a LED serial port tester.
Forgot to mention: the rate at which the control line flip-flops is dependent on the baud rate - the higher the baud rate, the faster the flip-flop; it must be syncronised with the baud rate clock?
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