title: RS232 handshaking - what happens in detail?
body: <p>Can anyone share with me any information on what <em>exactly</em> happens (or is meant to happen...) in RS232 communication when the status of the RTS or CTS line is changed?</p>
  
  <p>I'm working on an application where a PC, which interfaces to the serial port via Qt's QextSerialPort library, communicates with an Atmel AVR microcontroller. From time to time the microcontroller must do things (check ADCs, time precise intervals etc.) which require it to disable its internal interrupts and therefore shut down its UART port temporarily. I'm using RTS/CTS handshaking so that the AVR can signal to the PC when it is about to close its port by putting its RTS line high, and signal the re-opening of the port by bringing RTS low again. </p>
  
  <p>Basically this functions well, but I'm still unclear what is meant to happen if RTS is set high while there is a byte halfway through being transmitted in either direction. On the AVR side I can control things at a very low level, but on the PC side I just put QextSerialPort into hardware flow control mode, which causes it to do whatever the underlying Windows functions do. I'm wondering if a behavioural mismatch here may be the explanation for occasional glitches I get in the transmission.</p>