Gsm modem with AT89C51

[amit kulkarni]

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:

 

<code>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<code>

 

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?

[AJISH ALFRED]

Hi Amith,

Why don’t you post a diagram? It would have been more easy for us to find out the problem.

[amit kulkarni]

 

we have drawn this circuit in paint. Drawing is not very good.

RS232 male connector is connected just to make it easy to make the connections…

 

Waiting for your reply 

wysiwyg_imageupload:7214:

[AJISH ALFRED]

The connection is alright. Make sure that you’ve made the ground common for both the MCU and the modem including max232.

[amit kulkarni]

The ground is common no problem with it….

why it is not working?

[nidhin.k]

hi….. 

 

   please use 11.0592MHz crystal…. it will work

[amit kulkarni]

it is not shown here in this diagram,but  i have connected it

[RAJI G]

first  verify  ur serial communication program and then proceed..

[amit kulkarni]

This problem has been Solved

 

Thank you all

[muneebullashariff]

what was the problem???

 

[Author]

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