GSM (Global System for Mobile communication) interfaced with microcontroller AT89S52. GSM is widely used mobile communication architecture used in most of the countries. This project/tutorial demonstrates the interfacing of microcontrollerAT89S52 with HyperTerminal and GSM module.

HyperTerminal is a Windows application. The AT commands are sent by the HyperTerminal to the GSM module. The Information Response and/or Result Codes are received at the microcontroller and retransmitted to the HyperTerminal by the controller. A GSM module has an RS232 interface for serial communication with an external peripheral. In this case, the transmit pin (Tx) of the computer’s Serial port is connected with the receive pin (Rx) of the GSM module’s RS-232 interface. The transmit pin (Tx) of the RS-232 of GSM module is connected to receive pin (Rx) of microcontroller’s serial transmission pin. And the serial transmit pin of the microcontroller is connected to the receive pin of the computer’s Serial port. Therefore the commands and their results are transmitted and received in a triangular fashion as depicted below.

The microcontroller is programmed to receive and transmit data at a baud rate of 9600. The controller can receive data signals either by polling or by making use of serial interrupt (ES). Serial interrupt has been explained in interrupt programming. In polling, the controller continuously scans serial port for incoming data from the GSM module.