I am interfacing 8051 and sim900 for my project purpose. I am able to send message from my sim900 when interfaced with PC in hyperterminal using AT Commands. After programming using Keil in 8051 board i am able to get the same AT commands in hyperterminal when checked from the board output, But still when i connect both of them 8051 and sim900 ,the modem(sim900) is not sending any sms Can any one help me by sending me the complete source code for reading and sending sms using sim900 and 8051?