Question

I have got a task of sending hexadecimal data to my COMPORT in linux. I have written this simple C code, but it sends only a decimal number. Can anyone help me in sending an hexadecimal bit.

Here is the code I have written

#include <stdio.h>   /* Standard input/output definitions */
#include <string.h>  /* String function definitions */
#include <unistd.h>  /* UNIX standard function definitions */
#include <fcntl.h>   /* File control definitions */
#include <errno.h>   /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */

int number,n;
void main(void){
open_port(); 
}

  int open_port(void)
{
  int fd; /* File descriptor for the port */


  fd = open("/dev/ttyACM0", O_RDWR | O_NOCTTY | O_NDELAY);
  if (fd == -1)
  {

perror("open_port: Unable to open /dev/ttyACM0 - ");
  }
  else{
     printf("Port Opened successfully\n");
     number = 1;
     while(number!=55){
     scanf("%d",&number);
      n = write(fd, "ATZ\r", number);
     if (n < 0)
     fputs("write() of 4 bytes failed!\n", stderr);
     }


}

  return (fd);
}

Please help

Thanks in advance 🙂 🙂

Answer 1

write is defined as:

 ssize_t write(int fd, const void *buf, size_t count);

That is, it sends count bytes to fd from buf. In your case, the data is always the string “AZTR\r”, plus undefined data after that (if count is > 5). Your program sends neither hexadecimal nor decimal data.

Do you want to send binary data or a string of hexadecimal characters?

For option one, you can use: write(fd, somebuffer, len);, where some buffer is a pointer to any set of bytes (including ints, etc).

For option two, first convert your data to a hexadecimal string using sprintf with %02X as the format string, then proceed to write that data to the port.