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Interfacing the PIC18F452 with the GM862 module is relatively simple. What will be left is only the code that needs to be burned on the PIC. By the way,no full codes will be posted here. I will only post the codes that will give you a good kick start because I think it is better to understand than to copy and paste. And there is a Chinese saying:

Give a man a fish, you feed him for a day.
Teach him to fish, and you feed him for lifetime.

This is a sample project that I made and it only deals with making phone calls and I will upload other videos for SMS, GPRS and Data Call:

Now looking at the schematics you will find all the details on how to connect both the module and the PIC.

After doing the above connections, you need to start the module first and then initiate the baudrate that both of them will work on. The Telit module works on different values of baudrates (300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200). For me I shall work with baudrate 19200, but you can choose whatever baudrate that you want.

To start the module, you simply connect the ON_OFF pin to the ground for at least 1 sec (note: this pin is normally high). So you can do this by two ways. First way is to connect a switch and give the ON signal by hand, which is not a good idea. The second way which all of you will do, is to let the PIC18F452 do the job of turning the module ON. We will connect a transistor as shown in the schematic (PN2222A) such that when the base voltage is high, it allows the current to pass to the ground. So, you will need to make PORTC.PIN5 to be HIGH for 1 sec and then toggle it back to LOW (safety factor make it 1.1 sec).

So, after initializing the baudrate on the PIC you need to do the following at the start of your program:

while(recieved_serial!='AT;\nOK\r\n'){
send_serial('AT\r');
delay_ms(300);   //Delay 300 mSec
}

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Now we can start working with the GM862 module. Before connecting the microcontroller we have to make sure that the module itself turns on. Basically, what we will do is connect the following pins:

Pin 1,3,5,7 (Vbatt) ——to——> Vdd

Pin 2,4,8 (GND) ——to——> Ground

Pin 45 (RTS) ——to——> Ground

For us to debug this module, we will connect both the STATUS_LED (Pin 39) and PWRMON (Pin 21). These are output pins used to make sure that the module turns ON, look at the schematic to see how we connect the LEDs on these pins. Also, we will connect a normally opened switch where one side is connected to the ground while the other side is connected to the module pin 17 (ON_OFF).

Note in the schematic there are two extra pins (pin 51 & pin 52). These pins I added because when you use the Mikroelektronika board it will come with 52 pins (2 extra pins that are Not Connected – NC).

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