How to send AT command to a Modem using a Microcontrollers

  /*Header*****************************************************
Microcontroller=16f877
Clock=10 Mhz
Project Title:Air Pollution Control Using GSM/GPRS
Developed By:Sathiesh Kumar.V
Date:31/01/2010*/
void Calculation(unsigned int ) ;
void Gsm_SMS_Init();
void Gsm_SMS_Read();
void Gsm_SMS_Send();
// LCD module connections
sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;
sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;
// End LCD module connections
 
unsigned char ch;                    //
char Receive;
unsigned int adc_rd;                 // Declare variables
char *text;                          //
long tlong;                          //
unsigned int i,j;
char return_gsm[2];
char Gsm_Receive[100];
char Gsm_Msg[10];
char uart_rd[]="AT";
char uart_rd1[]="AT+CMGF=1";
char uart_rd2[]="AT+CMGR=1" ;
char uart_rd3[]="AT+CMGS=";
char Mobile_No[]="+919444721638" ;
char Send_Msg[]="@ON";
void main()
{
    INTCON = 0;                      // All interrupts disabled
    ADCON1 = 0x82;                   // A/D voltage reference is VCC
    TRISA = 0xFF;                    // All port A pins are configured as inputs
    TRISC=0x80;
    Delay_ms(2000);                    // Rest of pins are configured as digital
    UART1_Init(9600);              // Initialize UART module at 9600 bps
    Delay_ms(100);                 // Wait for UART module to stabilize
    Lcd_Init();                      // LCD display initialization
    Lcd_Cmd(_LCD_CURSOR_OFF);        // LCD command (cursor off)
    Lcd_Cmd(_LCD_CLEAR);             // LCD command (clear LCD)
 
    text = "Air Pollution ";       // Define the first message
    Lcd_Out(1,1,text);               // Write the first message in the first line
    delay_ms(500);
    text = "Sensor Value";            // Define the second message
    Lcd_Out(2,1,text);               // Define the first message
    delay_ms(500);
    Lcd_Cmd(_LCD_CLEAR);
 
 
    text = "GSM";               // Define the third message
 
   while (1)
   {
       Lcd_Out(1,1,text);               // Define the first message
       delay_ms(500);
       Lcd_Cmd(_LCD_CLEAR);
       Gsm_SMS_Init();
   }
}
 
void Gsm_SMS_Init()
{
if (UART1_Tx_Idle() == 1)
       {
         Lcd_Out(2,1,"AT");               // Define the first message
         delay_ms(500);
         Lcd_Cmd(_LCD_CLEAR);
 
         for(i=0;i<=1;i++)
          {
          UART1_Write(uart_rd[i]);           //AT
          }
        UART1_Write(0x0D);                   //Enter
 
        //delay_ms(5000);
        while(1)
        {
           Lcd_Out(2,1,"In while");               // Define the first message
           delay_ms(500);
           Lcd_Cmd(_LCD_CLEAR);
 
         if (UART1_Data_Ready())
        {                         // If data is received,
      Lcd_Out(2,1,"In IF");               // Define the first message
           delay_ms(500);
           Lcd_Cmd(_LCD_CLEAR);
 
          for(i=0;i<=1;i++)
          {
           return_gsm[i] = UART1_Read();      //   read the received data, Received OK
          }
           Lcd_Out(2,1,"OK");               // Define the first message
           delay_ms(500);
           Lcd_Cmd(_LCD_CLEAR);
 
          /* UART1_Write(return_gsm[0]);
           Lcd_Out(2,1,"OK RESEND");               // Define the first message
           delay_ms(500);
           Lcd_Cmd(_LCD_CLEAR);  */
 
          // UART1_Write(return_gsm[1]);
        }
        }
        /*if(return_gsm[0]==0x4F && return_gsm[1]==0x4B)
          {
            if (UART1_Tx_Idle() == 1)
            {
               for(i=0;i<=8;i++)
                {
                 UART1_Write(uart_rd1[i]);   //AT+CMGF=1
                }
               UART1_Write(0x0D);            //Enter
               Lcd_Out(1,1,"AT+CMGF=1");
               delay_ms(500);
               Lcd_Cmd(_LCD_CLEAR);
            }
            if (UART1_Data_Ready())
            {                             // If data is received,
                for(i=0;i<=1;i++)
                 {
                   return_gsm[i] = UART1_Read();      //   read the received data,OK
                 }
                 Lcd_Out(2,1,"Received OK");
                 delay_ms(500);
                 Lcd_Cmd(_LCD_CLEAR);
            }
                }  */
           }
  }Last edited by bryan1; 1st January