usart transmission problem

[kingshuk basu]

i am facing a problem with data transmission while using the usart module of 16f877a.

the data is being sent continuously even though the program is for sending data once only…………………..

plzzzzzzzzzz help.its urgent.this my program:

 

---

main

---

#include <htc.h>

#include “usart.h”

 

void gsm_cmd(unsigned char *);

void Delay_ms(unsigned char);

 

unsigned char value=0;

int i=0,j,k;

unsigned char *sms_format=”AT+CMGF=1″;

unsigned char *sms_write=”AT+CMGS=”9038940850″”;  // 10-Digit Mobile Number

unsigned char *sms=”Hello”;

unsigned char *sms_report=”SMS Sent…”;

unsigned char sms_terminate=0x1A;

unsigned char enter=0x0D;

unsigned char *data;

 

void main()

{

INTCON=0; // purpose of disabling the interrupts.

 

init_comms(); // set up the USART – settings defined in usart.h

 

gsm_cmd(sms_format);

 

Delay_ms(1000);

 

gsm_cmd(sms_write);

 

Delay_ms(1000);

 

gsm_cmd(sms);

Delay_ms(1000);

putch(0x1A);

Delay_ms(1000);

while(1);

}

 

void Delay_ms(unsigned char d)

{

while(d–);

}

 

void gsm_cmd(unsigned char *string)

{

int i=0;j=0;

while(string!=’’)

{

 

if(string==0x5C) // Not to send ” cahracter

i++;

putch(string); // Send by serial communication

i++;

 

}

 

putch(enter); // Send ASCII code for ‘Enter’ key

 

}

 

 

 

 

 

 

#include <htc.h>

#include <stdio.h>

#include “usart.h”

 

void putch(unsigned char byte) 

{

/* output one byte */

TXREG = byte;

  while(!TXIF); /* set when register is empty */

 

 

}

 

unsigned char getch()

{

/* retrieve one byte */

while(!RCIF) /* set when register is not empty */

continue;

return RCREG;

}

 

 

unsigned char

getche(void)

{

unsigned char c;

putch(c = getch());

return c;

}

[AJISH ALFRED]

Hi Kingshuk,

You haven’t written anything inside an infinite loop, but you can see the data being sent again and again.

Most probably your controller is getting restarted again and again after sending some data, that’s why you feel that the controller is continuosly sending data.

The reason for such an issue is always related with memory shortage. You might be either trying to allocate memory which is not avilable at the moment or trying to access memory which has not been allocated (using pointers).

This is basically run time error. Suggest you to thoroughly analyse your pointer usage.

 

For example in the following function;

 

void gsm_cmd(unsigned char *string)

{

int i=0;j=0;

while(string!=”)

{

 

if(string==0x5C) // Not to send ” cahracter

   i++;

else                          //#### TRY PUT AN ELSE HERE ####

   putch(string); // Send by serial communication

i++;

 

}

 

Try this also; change to ‘const char’

const char *sms_format=”AT+CMGF=1″;

const char *sms_write=”AT+CMGS=”9038940850″”;  // 10-Digit Mobile Number

const char *sms=”Hello”;

const char *sms_report=”SMS Sent…”;

Change to this type in function defenitions and wherever required.

 

 

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