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8051 interfacing with sim300

varun bhat

i am able to send msg from gsm to the mobile phone but am not able to receive data from the GSM.
eg..in this code when i send AT to the gsm , i get garbage value on the LCD instead of OK..but with the hyperterminal, the communication is proper with both the 8051 and GSM.

#include<stdio.h>
#include<at89x51.h>
#define port P1
#define dataport P2                             // Data port for LCD
sbit rs = port^2;
sbit rw = port^3;
sbit en = port^4;
 int p;
 unsigned char msg[20];
//generates delay in milli seconds
void delay_ms(unsigned int i)
{
unsigned int j;
        while(i-->0)
        {
                for(j=0;j<500;j++)
                {
                        ;
                }
        }
}

void command(unsigned char dost)
   {
   dataport=dost;                  //put the value on pin
   rs=0;
   rw=0;
   en=1;         //strobe the enable pin
   delay_ms(5);
   en=0;
   }



void lcddisplay(unsigned char word)
   {
   dataport=word;           //put the value on pin
   rs=1;
   rw=0;
   en=1;          //strobe the enable pin
   delay_ms(5);
   en=0;
   }

                void lcd_data_string(unsigned char *str)        // Function to display string on LCD
{
        int i=0;
        while(str[i]!='\0')
        {
          lcddisplay(str[i]);
          i++;
          delay_ms(1);
        }
        return;
}

//Function to initialize RS232 Serial Port
void serial_init()
{
        SCON=0x50;   //setup for 8-bit data
        TMOD=0x20;       //setup timer 1 for auto-reload
        TH1=0xfd; //Baud Rate 9600
                TL1=0xfd;
        TR1=1;       //turn on timer 1
        TI=1;            //indicate ready to transmit
}



//This function displays a null-terminated string on the RS232 port
void send_serial(unsigned char *s)
{
while(*s!=0x0)
{
SBUF=*s;
while(!TI)
{
}
TI=0;
s++;
}
}

int i;

void tx0(unsigned char x) //send data to serial port 0
{
EA=0;
SBUF=x;
while(TI==0);
TI=0;
EA=1;
}
void lcd()
{
        command(0x38);                                          // For using 8-bit 2 row LCD
        delay_ms(1);
        command(0x0F);                                          // For display on cursor blinking
        delay_ms(1);
        command(0x80);                                          // Set the cursor on first position of LCD
        delay_ms(1);
}
    char receive(void)
   { // unsigned char m;
        while (RI != 1) {;}     //wait to receive data

 msg[++p]=SBUF;           // save value of data
 RI=0;
 return (msg[p]);

}

void main()
{
p=(-1);
delay_ms(80);
lcd();
delay_ms(50);
serial_init();   //Initialize Serial port.

while(1)
{ int m;
send_serial(" AT");
delay_ms(400);
tx0(0x0D);

m=receive();
command(0x06);
lcddisplay(m);

}
}