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I have been trying to interface GSM using the code and circuit from this link, since 2 days. only difference is that I am using AT89S52 and SIM900A module, but I am not getting any response like OK on LCD, can anybody guide me in right direction?

Can different 8051 controller be the problem? I am pasting the code here:

// Program to Interface GSM Module with 8051 microcontroller (AT89C51) without using PC

#include<reg51.h>
#define port P1
#define dataport P2             // Data port for LCD
sbit rs = port^2;
sbit rw = port^3;
sbit en = port^4;
int count,i;
unsigned char check,str[15];
bit check_space;

void init_serial()          // Initialize serial port
{
    TMOD=0x20;          // Mode2
    TH1=0xfd;           // 9600 baud
    SCON=0x50;          // Serial mode=1 ,8-Bit data,1 Stop bit ,1 Start bit, Receiving on
    TR1=1;              // Start timer
}
void delay(unsigned int msec)       // Function for delay
{
    int i,j;
    for(i=0;i<msec;i++)
        for(j=0; j<1275; j++);
}

void lcd_cmd(unsigned char item)        // Function to send command on LCD
{
    dataport = item;
    rs= 0;
    rw=0;
    en=1;
    delay(1);
    en=0;
    return;
} 

void lcd_data(unsigned char item)       // Function to display character on LCD
{
    dataport = item;
    rs= 1;
    rw=0;
    en=1;
    delay(1);
    en=0;
    return;
}

void lcd_data_string(unsigned char *str)    // Function to display string on LCD
{
    int i=0;
    while(str[i]!='\0')
    {
      lcd_data(str[i]);               
      i++;
      delay(10);                                        
    }
    return; 
}
void lcd()
{
    lcd_cmd(0x38);                      // For using 8-bit 2 row LCD 
    delay(5);                                   
    lcd_cmd(0x0F);                          // For display on cursor blinking
    delay(5);                                   
    lcd_cmd(0x80);                      // Set the cursor on first position of LCD 
    delay(5);                                   
}

void transmit_data(unsigned char str)   // Function to transmit data through serial port
{
    SBUF=str;               //Store data in SBUF
    while(TI==0);               //Wait till data transmits
    TI=0;             
}

 void receive_data()  interrupt 4   // Function to recieve data serialy from RS232 into microcontroller
 {   
    RI=0;
    str[++count]=SBUF;          //Read SBUF

 }

unsigned char byte_check()      // Function to check carraige return and new line character
{
    switch(str[0])
    {
        case 0x0a:
        {               // Return 0x00 for new line
        return 0x00;
        break ;
        }
        case 0x0d:
        {               // Return 0x01 for carriage return
        return 0x01;
        break ;
        }
        default :return 0x02 ;      // Return 0x02 for characters except new line and carriage return
    }
}

void main()
{ 
    lcd();                              // Initialize LCD
    init_serial();                          // Initialize serial port
    count=(-1);
    delay(500);
    lcd_data_string("Ready");
    delay(10);                              
    lcd_cmd(0x01);  
    IE=0x94; 
    transmit_data('A');                 // Transmit 'A' to serial port
    delay(1);
    transmit_data('T');                 // Transmit 'T' to serial port
    delay(1);
    transmit_data(0x0d);                    // Transmit carriage return to serial port
    delay(50);
    while(1)
    {
        if(count>=0)
        {
            check=byte_check();             // Check the character
            if(check!=0x00)
            {           
                if(check==0x01)
                {
                    if(check_space==1)      // Check previous character
                    {
                        lcd_data(0x20);
                        check_space=0;
                    }
                }
                else    
                {
                    lcd_data(str[0]);
                    check_space=1;
                }
            }
            count--;                   
            for(i=0;i<count;i++)            // Shift the whole array to one left
            {
                str[i]=str[i+1];
            }
        }
    }
}
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  • \$\begingroup\$ do you see cursor on the left-most side? \$\endgroup\$ – MaMba Aug 3 '15 at 15:11
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Well most of the things are same for the AT89S51 and At89S52 but yet they way header files are implemented differs hence the way the constants like TMOD,TR1,TF1 are defined in reg51.h may be different for the AT89S52 they are defined by their hex address which may vary in these header files,hence I would adice you to use 52 header file,Lets me know if trouble still occurs.

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  • \$\begingroup\$ I have used reg52.h but its still not working, and the code I have pasted is for AT89C51 not S51, I am still trying with no luck \$\endgroup\$ – aayush Aug 3 '15 at 8:06

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