GSM modem not responding when commands send by 8051

[bsaurabh]

Iam facing new problem. i have programed 8051 to send the commands to GSM modem to send SMS. I have connected the TX pin of 8051 board to RX pin of modem & the RX pin of 8051 board to TX pin.also i have short the GND pins.But there is no response. the controller is sending the instructions properly if we see it on hyperterminal. but the modem is not giving any response even for simple command like "AT".:-(

How sholud i connect the modem to 8051 board?????
should i keep open the other pins(RTS, CTS,DTR, DCD, DSR) of DB9 connector on modem?????
what should I do of flow control in modem???????????
or should I send some instruction to modem at first?????

 

[nandhu015]

What is the baud rate, check and confirm it is 9600 (normally all modems by default)

 

[electronicsbasecom]

Which modem? Since there is no AT answer means that you probably have hardware problem. Check your serial communication without modem. Check did you use a proper pins of modem, in some datasheets Tx and Rx on modem are actually Tx and Rx of MCU.

 

[torana]

which modem u r using. in modem board is there any max232 IC. another thing u must connect ane max232 ic with microcontroller then to modem board.