OT: Modem Interfacing to PIC

[Victor]

I like to interface an external 56K modem to PIC, with minimum I/O and wire connection, beside TX,RX, GND, what other signal (RTS,DSR & etc) must be connect for it to work correctly ?

I know one signal must have (DTR?) to wake up the modem? But I can't remember which ....

[Ttelmah]

Just loop DSR back to DTR at the modem's plug, and CTS to RTS. If you want to drive data into the modem faster than it can send it across the link, then you will need to monitor the CTR connection, to 'know' when the modem is signalling that it's buffer is full. Similarly, if the link from the modem to you, is potentially faster than you can handle the data, then you will need to break the CTS-RTS connection, and actually generate a 'RTS' signal, to control the data flow.

Best Wishes