Can you please tell me how to interface GSM modem (sim 300) to microcontroller (AT89C51)to send sms?

I need assembly program for the same..

I have prepared my own but it is not working:

here it is:

ORG 0000H
        MOV TMOD,#20H               //TIMER 1, MODE 2
        MOV TH1,#-3                //9600 BAUD RATE
        MOV SCON,#50H            //8 BIT, 1 STOP, EN ENABLED
        SETB TR1
                
        MOV DPTR,#MSG1
        ACALL H1
        ACALL DELAY
        MOV DPTR,#MSG2
        ACALL H1
        ACALL DELAY
        MOV DPTR,#MSG3
        ACALL H1
        ACALL DELAY
        MOV DPTR,#MSG4
        ACALL H1
        ACALL DELAY
        MOV DPTR,#MSG5
        ACALL H1
        ACALL DELAY
STAY: SJAMP STAY
H1:      CLR A
        MOVC A,@A+DPTR
        JZ B1
        ACALL SEND
        INC DPTR
        SJMP H1
B1:
        RET
SEND:     MOV SBUF,A
H2:     JNB TI,H2
        CLR TI
        RET
DELAY:  MOV R3,#50H
HERE2:  MOV R4,#50H
HERE:    DJNZ R4,HERE
        DJNZ R3,HERE2
        RET
    

ORG 300H
MSG1: DB "AT",0DH
      DB 0H
MSG2: DB "AT+CMGF=1",0DH
      DB 0H
MSG3: DB "ATE=0",0DH
      DB 0H
MSG4: DB "AT+CMGS=",'"8149111111"',0DH
      DB 0H
MSG5: DB "TEXT",0X1A
      DB 0H

      END

connections:
GSM modem has following on-board connections:

MAX232----->> RS232 (Female connector)

pin 7 ---> Pin 2
pin 8 ---> Pin 3

So i have done following connections after this:

RS232 (Female connector) --->> RE232(PCB male connector ) ( This o did because it was difficult to take connections from on-board Female connetor)

I took out following pins from RS232 male connector and connected to microcontroller:

RS232(PCB male connector ) ---> AT89C51
Pin 2 --> Pin 11
Pin 3--> Pin 10
Pin 5 Grounded.

Rest AT89C51 connetions:

Crystal oscillator 12 Mhz.
EN (Pin 31) -VCC
Pin 40-- VCC
Pin 20-- Gnd


Are these connetions are correct??
why my program is not working ??


can any one tell me assembly program to interface the same?

 

How about supplying a schematic. That will allow us to be able to see your connections instead of read about them.

 

How about supplying a schematic. That will allow us to be able to see your connections instead of read about them.

i think . can help you

 

here is my circuit diagram...

please tell me where i am going wrong :|