serial_port_example

test example for serial port

steal from http://stackoverflow.com/questions/6947413/how-to-open-read-and-write-from-serial-port-in-c

#include <errno.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <termios.h> #include <unistd.h>

int set_interface_attribs(int fd, int speed) { struct termios tty;

if (tcgetattr(fd, &tty) < 0) {
    printf("Error from tcgetattr: %s\n", strerror(errno));
    return -1;
}

cfsetospeed(&tty, (speed_t)speed);
cfsetispeed(&tty, (speed_t)speed);

tty.c_cflag |= (CLOCAL | CREAD);    /* ignore modem controls */
tty.c_cflag &= ~CSIZE;
tty.c_cflag |= CS8;         /* 8-bit characters */
tty.c_cflag &= ~PARENB;     /* no parity bit */
tty.c_cflag &= ~CSTOPB;     /* only need 1 stop bit */
tty.c_cflag &= ~CRTSCTS;    /* no hardware flowcontrol */

/* setup for non-canonical mode */
tty.c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);
tty.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
tty.c_oflag &= ~OPOST;

/* fetch bytes as they become available */
tty.c_cc[VMIN] = 1;
tty.c_cc[VTIME] = 1;

if (tcsetattr(fd, TCSANOW, &tty) != 0) {
    printf("Error from tcsetattr: %s\n", strerror(errno));
    return -1;
}
return 0;

}

void set_mincount(int fd, int mcount) { struct termios tty;

if (tcgetattr(fd, &tty) < 0) {
    printf("Error tcgetattr: %s\n", strerror(errno));
    return;
}

tty.c_cc[VMIN] = mcount ? 1 : 0;
tty.c_cc[VTIME] = 5;        /* half second timer */

if (tcsetattr(fd, TCSANOW, &tty) < 0)
    printf("Error tcsetattr: %s\n", strerror(errno));

}

int main() { char *portname = "/dev/ttyUSB0"; int fd; int wlen;

fd = open(portname, O_RDWR | O_NOCTTY | O_SYNC);
if (fd < 0) {
    printf("Error opening %s: %s\n", portname, strerror(errno));
    return -1;
}
/*baudrate 115200, 8 bits, no parity, 1 stop bit */
set_interface_attribs(fd, B9600);
//set_mincount(fd, 0);                /* set to pure timed read */

/* simple output */
wlen = write(fd, "$001,01&\n", 9);
if (wlen != 9) {
    printf("Error from write: %d, %d\n", wlen, errno);
}
tcdrain(fd);    /* delay for output */


/* simple noncanonical input */
do {
    unsigned char buf[80];
    int rdlen;

    rdlen = read(fd, buf, sizeof(buf) - 1);
    if (rdlen > 0) {

#ifdef DISPLAY_STRING buf[rdlen] = 0; printf("Read %d: "%s"\n", rdlen, buf); #else /* display hex */ unsigned char *p; printf("Read %d:", rdlen); for (p = buf; rdlen-- > 0; p++) printf(" 0x%x", p); printf("\n"); #endif } else if (rdlen < 0) { printf("Error from read: %d: %s\n", rdlen, strerror(errno)); } / repeat read to get full message */ } while (1); }

test ok on RS485串口表LED数码管显示屏显示模块PLC + usb转rs485 usb转485