Hi
Some of the UARTs support RTS/CTS lines which have capabilities of automatically controlling flow control:
http://www.utasker.com/forum/index.php?topic=105.msg424#msg424The CTS interrupt capability allows interrupt driven flow control too.
Since CD input is generally more of an informative nature rather than than controlling data flow (with some reaction constraints) it doesn't usually merit a dedicated modem control signal at the UART.
The same function can be achieved by any free Edge Port line. When there are no edge ports free further interrupt capability is possible by using timers in edge-capture more and even the interrupt driven trigger functionality of the ADC inputs. More generally polling any free GPIO is often adequate as well.
Regards
Mark
www.uTasker.com