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PIC 18F8722 and Modem connection via rs232

 
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ujjwal19



Joined: 01 Mar 2008
Posts: 3

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PIC 18F8722 and Modem connection via rs232
PostPosted: Mon Mar 31, 2008 9:21 am     Reply with quote
Hi,
My PIC is communication to the PC and the MODEM is communicating to the PC individually via rs232. I get a response as "OK" or "ERROR" from the modem when i send a command "AT" to the modem from the PIC using rs232.

But i am not able to get the response when i connect the PIC and the Modem together. I have taken care of the handshaking signals and the cross over cable issues. Am using both the RS232 in the PIC, one to send the command to the PIC and the other to monitor the response coming back from the PIC.

i have a simple test code as follows. Could anyone please suggest me what i am doing wrong and help me with the code, since PIC and Modem is not communicating at all. Here i am just trying to capture the "O" or the "E". The modem baud rate and other settings and the PIC settings are set all same.
Code:
#include <18f8722.h>
#fuses HS,NOLVP,NOWDT
#use delay (clock=20000000)


#use rs232 (baud=19200, xmit=PIN_C6, rcv=PIN_C7, stream=PORT1)
#use rs232 (baud=19200, xmit=PIN_G1, rcv=PIN_G2, stream=PORT2)

void main() {
  char response;
     
   setup_timer_0(RTCC_INTERNAL);
   while(TRUE) {
      fputc(0x41,PORT2); //A in Hex
      fputc(0x54,PORT2); //T in Hex
      fputc(0x0D,PORT2); //Carriage return
     
      response=fgetc(PORT2);
     
      fputc(response,PORT1);
   }
}

Thank you very much.

Regards,
Ujjwal
Matro
Guest
PostPosted: Mon Mar 31, 2008 9:30 am     Reply with quote
Are you fully sure of your hardware (especially that RX and TX lines are not inverted)?
Did you check that baudrate, parity, stop bit length were the same on both sides?
Are the voltage levels compatible?

Matro.
ujjwal19



Joined: 01 Mar 2008
Posts: 3

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PostPosted: Mon Mar 31, 2008 10:52 am     Reply with quote
thanks a lot for the reply. Yes, i did check the Rx and Tx and they are not inverted. Also the parity , baudrate and the stop bit lengths are same.
Since the pIC and Modem were communicating with the PC individually via the RS 232 so i thought the voltage levels will be fine. But will check that once.

Do u think my code is fine or is something wrong there??

Thanks a lot.

regards
ujjwal
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