Interfacin Arduino with GSM Modem

I am using a GSM Modem to send and receive SMSs. I am using serial RX interrupt service routine therefore I cannot use the arduino’s built in serial functions.

I managed to read and write string to and from the serial monitor , I also wrote stings from the arduino to the PC using the hyper terminal , therefore the MAX232 circuit is ok.

But when I connect the Arduino to the modem nothin happens. The modem works fine with hyperTerminal therefore there no problems with that. Any suggestions.

My toughts are that I am messing something with the CR or NL any ideas are welcome

Thanks

StepTester.ino (967 Bytes)