This document discusses interfacing a GSM module with an 8051 microcontroller (AT89C51) without using a PC. It includes a circuit diagram and code to initialize serial communication between the GSM and 8051, transmit and receive data, and display received messages on an LCD. The code transmits the characters "AT" followed by a carriage return to the GSM module to check communication, then displays any responses on the LCD, shifting characters left and adding spaces between words.

1. 2/28/2014 Interface GSM with 8051 Microcontroller (AT89C51)
http://www.engineersgarage.com/microcontroller/8051projects/interfacing-gsm-8051-microcontroller-circuit-code 1/4
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Interfacing GSM Module with 8051
microcontroller (AT89C51) without
using PC
//ProgramtoInterfaceGSMModulewith8051microcontroller(AT89C51)withoutusin
#include<reg51.h>
#defineportP1
#definedataportP2 //DataportforLCD
sbitrs=port^2;
sbitrw=port^3;
sbiten=port^4;
intcount,i;
unsignedcharcheck,str[15];
bitcheck_space;
voidinit_serial() //Initializeserialport
{
TMOD=0x20; //Mode2
TH1=0xfd; //9600baud
SCON=0x50; //Serialmode=1,8-Bitdata,1Stopbit,1
TR1=1; //Starttimer
}
voiddelay(unsignedintmsec) //Functionfordelay
{
inti,j;
for(i=0;i<msec;i++)
for(j=0;j<1275;j++);
}
voidlcd_cmd(unsignedcharitem) //FunctiontosendcommandonLCD
{
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2. 2/28/2014 Interface GSM with 8051 Microcontroller (AT89C51)
http://www.engineersgarage.com/microcontroller/8051projects/interfacing-gsm-8051-microcontroller-circuit-code 2/4
dataport=item;
rs=0;
rw=0;
en=1;
delay(1);
en=0;
return;
}
voidlcd_data(unsignedcharitem) //Functiontodisplaycharacteron
{
dataport=item;
rs=1;
rw=0;
en=1;
delay(1);
en=0;
return;
}
voidlcd_data_string(unsignedchar*str) //FunctiontodisplaystringonLC
{
inti=0;
while(str[i]!='0')
{
lcd_data(str[i]);
i++;
delay(10);
}
return;
}
voidlcd()
{
lcd_cmd(0x38); //Forusing8-bit
delay(5);
lcd_cmd(0x0F); //Fordisplayonc
delay(5);
lcd_cmd(0x80); //Setthecursoro
delay(5);
}
voidtransmit_data(unsignedcharstr) //Functiontotransmitdatathroughserial
{
SBUF=str; //StoredatainSBUF
while(TI==0); //Waittilldatatransmits
TI=0;
}
voidreceive_data() interrupt4 //FunctiontorecievedataserialyfromRS
{
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3. 2/28/2014 Interface GSM with 8051 Microcontroller (AT89C51)
http://www.engineersgarage.com/microcontroller/8051projects/interfacing-gsm-8051-microcontroller-circuit-code 3/4
RI=0;
str[++count]=SBUF; //ReadSBUF
}
unsignedcharbyte_check() //Functiontocheckcarraigereturnandne
{
switch(str[0])
{
case0x0a:
{ //Return0x00fornewline
return0x00;
break;
}
case0x0d:
{ //Return0x01forcarriagereturn
return0x01;
break;
}
default:return0x02; //Return0x02forcharactersexcep
}
}
voidmain()
{
lcd(); //Initiali
init_serial(); //Initiali
count=(-1);
delay(500);
lcd_data_string("Ready");
delay(10);
lcd_cmd(0x01);
IE=0x94;
transmit_data('A'); //Transmit'A'to
delay(1);
transmit_data('T'); //Transmit'T'to
delay(1);
transmit_data(0x0d); //Transmitcarriag
delay(50);
while(1)
{
if(count>=0)
{
check=byte_check(); //Checkth
if(check!=0x00)
{
if(check==0x01)
{
if(check_space==1) //Checkpr
{
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lcd_data(0x20);
check_space=0;
}
}
else
{
lcd_data(str[0]);
check_space=1;
}
}
count--;
for(i=0;i<count;i++) //Shiftthewhole
{
str[i]=str[i+1];
}
}
}
}
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