AT commands are a list of commands that you can use to communicate with any kind of a mobile phone or a GSM module serially. First you have to identify the GSM module and it’s own AT commands list first. In a case that you don’t have a GSM module, you can use a basic mobile phone connected to the pc as a gsm module. (note it’s not working stand alone, always with the PC)
After connecting the mobile/GSM module to the PC via serial or USB try to communicate with it with using a hyper terminal(win XP) or Putty client(any OS). Download putty from here.
Same way find the serial port of the GSM module and try to communicate.
There are various at commands to select sms mode, dial a number, Bluetooth(mobiles with bluetooth), access sim memory and all operations.
Ex: ATD 0711234567;
//dials the number
Hang the phone
Note : if you are using a mobile phone, there’s a big possibility of it’s not supporting the text mode but the PDU mode. To check the format it supports, type AT+CMGF=? in the terminal. If the device returns “0” it supports only the pdu mode. That implies you can’t send a text as it’s but need to convert into PDU format.
If it returns 1 or 0,1 it says it supports text mode and both respectively.
Interfacing with the IC
After you are done with your mobile/gsm module and understand the AT commands, use ISIS to simulate the circuit.
AT commands can be issued to the device via HSEROUT/TX pin of the IC. And will be received by the RX pin of the device. (Module or the phone. If it’s a micro usb phone, u don’t need to worry about the TX,RX of the device)
To output a command to the device using hardware serial port of the PIC,
hserout [“ATD 711234567;”,13,10];
//13 : carriage return , 10: new line character