i want to interface GSM modem with 8051 microcontroller with yhe use of RS232 so plese give me connection diagram and discription of this inter facing. also discription of AT command set is required .
"BOLD"
Maybe you should have used a summary of HOPEFUL
Or I know I'm pushing my luck, but ...
The world doesn't have just "one modem". And not just "one 8051".
So there can't be just one connection diagram. And not one single AT command-set document.
If you do have a modem using UART for access, then it is up to you to figure out if the modem have the correct signal voltages to interface directly with your microcontroller. If so, then it is up to you to figure out which signals are part of the serial port on the modem and on the 8051. And which of the signals you need.
You should obviously not have selected a modem unless you already have managed to retrieve a good set of documentation about it - both the hardware information, and the AT command-set documentation. If you did select a modem without documentation, then just unselect that modem, and find another.
In the end, your work is yours to do.
http://www.keil.com/forum/19613/