Hi, I use GSM Module(Wavecom 2686) to send SMS. Communication to the module is through the serial port (RXD,TXD).I tested the module by sending AT commands (as per the GSM Module Catalogue). Now I have to do the same using my uC(AT89S52). I tried to send the commands using printf function as given in the "Hello World" example. For this I initialised the controller for 9600 baud rate and other SFRs. Also included STDIO.H But it is not working and remains in the printf command without completing. What could be the reason? Pls note that I have very limited knowledge in programming.