Null Modem Sender

After installing null modem, then we are ready to send character data through serial port. I have an example of sending data through the null modem that we have prepared before. Lets have a look at the source code :

#include "termios.h" /*this file contains declaration of required functions and types*/
#include "stdio.h" /*you know what this is*/
#include "fcntl.h" /*this file constains declaration for O_RDWR and O_NOCTTY)*/
#include "time.h" /*this file contains time's operatives*/


int main(void)
    {
    int i, j, s;
    char t[9];
    time_t ttrs;
    struct tm *ti;
    int fd; /*variable of type integer used as descriptor to a serial port*/
    char c;
    struct termios termiosA; /*declaring a variable of type termios*/

    /* Turn on the null modem */
    fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY); /* I have done : sudo chmod 777 /dev/ttyS0 */


    /* We don't care about incoming bytes with parity on data input */
    termiosA.c_iflag = IGNPAR;

    /*
    Raw output.
    */
    termiosA.c_oflag = CR0; /* output modes */

    /*
    we are going to set a connection with serial port to the receiver (this computer is a sender)
    1. Baudrate is 4800 BPS (B9600)
    2. Enable RTS/CTS (hardware) flow control (CRTSCTS)
    3. Ignore modem control lines (CLOCAL)
    4. Character size mask is 8 (CS8)
    */
    termiosA.c_cflag = B4800 | CRTSCTS | CLOCAL | CS8; /* control flags
    */


    /* flush the modem line */
    tcflush(fd, TCIFLUSH);

    /* initiate the modem */
    tcsetattr(fd,TCSANOW,&termiosA);

    /* Now its time to send something. */
    i = 0;
    for (;;)
        {
        time(&ttrs);
        ti=localtime(&ttrs);
        if (s != ti->tm_sec)
            {
            printf("Sending time data : %s", t);
            sprintf(t, "%d:%d:%d\n", ti->tm_hour, ti->tm_min, ti->tm_sec);
            s = ti->tm_sec;
            for (j = 0; j < 9;j++)
                {
                write(fd, t[j], 1);
                }
            }
        }
    return 0;
    }