interfacing sim300 with 8051

[minujayakumar]

I am using AT89C52  controller in my project. I need to send message using sim300. sim300 is working properly when i connected to hyperterminal. I even tried connecting microcontroller to hyperterminal and it is also working properly. But when I connect microcontroller to sim300, it is not generating any message or call. Sim300 has inbuilt MAX232 IC and has RXD,TXD,GND pins. Should I connect these pins directly to the controller(10,11,20) or use MAX232 IC and RS232 externally? I tried both of them, but its not working. Can you provide me with correct circuit? When I run the program in proteus, I get different symbols in virtual terminal. Why I am getting like this?

This is the code i have used in my project.

#include<reg52.h>

void cmd(unsigned char *p)

{

while(*p)

{

SBUF=*p;

p++;

while(TI==0); 

TI = 0;

}

}

void main()

{

unsigned int i,j;

SCON = 0x52;    

TMOD = 0x20;   

TH1  = 0xFD;    

TR1= 1;  

 

cmd(” ATr”);

for(b=0;b<1000;b++);

cmd(” AT+CMGF=1″);

for(b=0;b<1000;b++);

cmd(” AT+CMGS “+918939xxxxxx””);

for(b=0;b<1000;b++);

cmd(” Hello “);

for(b=0;b<1000;b++);

SBUF = 0x1A; 

here: goto here;

}

 

[Ganesh Selvaraj]

Microcontroller works on TTL logic (logic high =5V) ans RS232 works with +12V …. connecting them directly will damge the system. If you have MAX232 IC on Modem and connecting through the RS232 port, then it is mandatory to have the same on other side also (on Microcontroller side).

 

And regarding your program, I’m not much familiar with 8051 Programming but what baud rate have you taken in this program? and did you set the same baudarate on proteus Virtual Terminal? Unexpected symbols are shown on the VT usually when there is a mismatch of baudrate.

[Author]

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