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    C serial port programming


    I have two c program files, which is send.c and read.c.

    Here is my send.c:
    #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 */
    /*
    * 'open_port()' - Open serial port 1.
    *
    * Returns the file descriptor on success or -1 on error.
    */
    int main(void)
    {
    int fd; /* File descriptor for the port */
    fd = open("/dev/ttyS1", O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd == -1)
    {
    // Could not open the port.
    perror("open_port: Unable to open /dev/ttyS1 - ");
    }
    else
    fcntl(fd, F_SETFL, 0);
    char *DATA="7E 40 09 00 BE EF 05 7D 5D 06 01 02 03 04 05 7E\r";
    int n = write(fd, DATA, strlen(DATA));
    if (n < 0)
    fputs("write() of bytes failed!\n", stderr);
    printf("Data is written...\n");
    return 0;
    }

    Here is my read.c
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <termios.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>

    /* baudrate settings are defined in <asm/termbits.h>, which is
    included by <termios.h> */
    #define BAUDRATE B115200
    /* change this definition for the correct port */
    #define MODEMDEVICE "/dev/ttyS0"
    #define _POSIX_SOURCE 1 /* POSIX compliant source */

    #define FALSE 0
    #define TRUE 1

    volatile int STOP=FALSE;

    main()
    {
    int fd,c, res;
    struct termios oldtio,newtio;
    char buf[255];
    /*
    Open modem device for reading and writing and not as controlling tty
    because we don't want to get killed if linenoise sends CTRL-C.
    */
    fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
    if (fd <0) {perror(MODEMDEVICE); exit(-1); }

    tcgetattr(fd,&oldtio); /* save current serial port settings */
    bzero(&newtio, sizeof(newtio)); /* clear struct for new port settings */

    /*
    BAUDRATE: Set bps rate. You could also use cfsetispeed and cfsetospeed.
    CRTSCTS : output hardware flow control (only used if the cable has
    all necessary lines. See sect. 7 of Serial-HOWTO)
    CS8 : 8n1 (8bit,no parity,1 stopbit)
    CLOCAL : local connection, no modem contol
    CREAD : enable receiving characters
    */
    newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;

    /*
    IGNPAR : ignore bytes with parity errors
    ICRNL : map CR to NL (otherwise a CR input on the other computer
    will not terminate input)
    otherwise make device raw (no other input processing)
    */
    newtio.c_iflag = IGNPAR | ICRNL;

    /*
    Raw output.
    */
    newtio.c_oflag = 0;

    /*
    ICANON : enable canonical input
    disable all echo functionality, and don't send signals to calling program
    */
    newtio.c_lflag = ICANON;

    /*
    initialize all control characters
    default values can be found in /usr/include/termios.h, and are given
    in the comments, but we don't need them here
    */
    newtio.c_cc[VINTR] = 0; /* Ctrl-c */
    newtio.c_cc[VQUIT] = 0; /* Ctrl-\ */
    newtio.c_cc[VERASE] = 0; /* del */
    newtio.c_cc[VKILL] = 0; /* @ */
    newtio.c_cc[VEOF] = 4; /* Ctrl-d */
    newtio.c_cc[VTIME] = 0; /* inter-character timer unused */
    newtio.c_cc[VMIN] = 1; /* blocking read until 1 character arrives */
    newtio.c_cc[VSWTC] = 0; /* '\0' */
    newtio.c_cc[VSTART] = 0; /* Ctrl-q */
    newtio.c_cc[VSTOP] = 0; /* Ctrl-s */
    newtio.c_cc[VSUSP] = 0; /* Ctrl-z */
    newtio.c_cc[VEOL] = 0; /* '\0' */
    newtio.c_cc[VREPRINT] = 0; /* Ctrl-r */
    newtio.c_cc[VDISCARD] = 0; /* Ctrl-u */
    newtio.c_cc[VWERASE] = 0; /* Ctrl-w */
    newtio.c_cc[VLNEXT] = 0; /* Ctrl-v */
    newtio.c_cc[VEOL2] = 0; /* '\0' */

    /*
    now clean the modem line and activate the settings for the port
    */
    tcflush(fd, TCIFLUSH);
    tcsetattr(fd,TCSANOW,&newtio);

    /*
    terminal settings done, now handle input
    In this example, inputting a 'z' at the beginning of a line will
    exit the program.
    */
    while (STOP==FALSE) { /* loop until we have a terminating condition */
    /* read blocks program execution until a line terminating character is
    input, even if more than 255 chars are input. If the number
    of characters read is smaller than the number of chars available,
    subsequent reads will return the remaining chars. res will be set
    to the actual number of characters actually read */
    res = read(fd,buf,255);
    buf[res]=0; /* set end of string, so we can printf */
    //printf(":%s:%d\n", buf, res);
    int bufsize = 46;
    int k=0;
    int i;
    for (i=0;i<bufsize;i++)
    {
    if (buf[i]=' ')
    {
    k++;
    }
    if (k==3)
    {
    printf("Proto %s\n", buf);
    }
    }
    //printf("%s", buf);
    //if (buf[0]=='z') STOP=TRUE;
    }
    /* restore the old port settings */
    tcsetattr(fd,TCSANOW,&oldtio);
    }

    The output is:
    Proto 40 09 00 BE EF 05 7D 5D 06 01 02 03 04 05 7E

    May I know how can I just print out and nicely with expected output "Proto = 40"?

    Thank you very much

    Comments on this post

    • mike65535 disagrees : Code tags please
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    Or to make it clearer, I have a send.c.
    I want to send: "7E 40 09 00 BE EF 05 7D 5D 06 01 02 03 04 05 7E".
    But at the read.c, I want "Proto = 40" as the output.
    Currently in my program, the output is:
    "Proto 40 09 00 BE EF 05 7D 5D 06 01 02 03 04 05 7E".
    Please help me...

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