Instead of sending commands from the HyperTerminal, AT commands are sent to the GSM/GPRS module by the microcontroller itself. In this case, the receive (Rx) and transmit (Tx) pin of the GSM module’s RS232 port are connected to the transmit (Tx) and receive (Rx) pin of AT89C51’s serial port, respectively. This eliminated the role of computer and just the controller’s circuit provides a complete user interface for the module.
The controller is programmed to send a fixed command ‘AT’ to the module. The command AT is used to check the communication with module. It returns a result code OK if the module and the controller are connected properly. If either of the module or SIM are not working, it returns a result code ERROR.
The program complexities for display of information responses and result codes on LCD mentioned in MC075 remain same here as well.