在 Ubuntu 下从串口读取和写入 USB 规模 [英] Read and Write from serial port under Ubuntu for USB scale

问题描述

我有一个通过 USB 连接到我的 Ubuntu 笔记本电脑的数字秤，我想从中读取测量值.串行协议非常简单(9600、8N1、ttyUSB0)，我可以通过终端使用腻子(VT100+)正确读取测量值.

I have a digital scale connected via USB to my Ubuntu laptop and I would like to read the measurements from it. The serial protocol is very simple (9600,8N1, ttyUSB0) and I'm able to correctly read the measurements by using putty (VT100+) from terminal.

秤需要接收命令

"READ<CR><LF>"

为了发送测量.每个测量都具有以下格式:

in order to send the measurement. Each measurement has this format:

01ST,GS,   2.5,kg<CR><LF>

例如，如果我测量的是 2.5Kg 的负载.

if, for example, I'm measuring a 2.5Kg load.

现在，我正在尝试从 C 应用程序发送 READ 命令，但我无法得到任何答案.

Now, I'm trying to send the READ command from a C application, but I'm not able to get any answer.

#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;
    printf("Opening the connection on serial port\n");
    fd = open(portname, O_RDWR | O_NOCTTY | O_SYNC);
    if (fd < 0) {
        printf("Error opening %s: %s\n", portname, strerror(errno));
        return -1;
    }
    /*baudrate 9600, 8 bits, no parity, 1 stop bit */
    set_interface_attribs(fd, B9600);
    //set_mincount(fd, 0);                /* set to pure timed read */

    /* simple output */
    printf("Sending the command READ\n");
    wlen = write(fd, "READ\n", 5);
    if (wlen != 5) {
        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) {

            buf[rdlen] = 0;
            printf("Read %d: \"%s\"\n", rdlen, buf);

        } else if (rdlen < 0) {
            printf("Error from read: %d: %s\n", rdlen, strerror(errno));
        } else {  /* rdlen == 0 */
            printf("Timeout from read\n");
        }               
        /* repeat read to get full message */
    } while (1);
}

你能帮我吗?谢谢！我是初学者，所以可能只是我看不到的愚蠢错误.

Can you help me, please? Thank you! I'm a beginner, so may be it's just a stupid error I cannot see.

但是，有没有其他更快的方法来获得相同的任务?

However, is there any other faster way to acquire the same task?

推荐答案

可能命令应该以回车符结束(不是你写的换行符):

Probably the command should be terminated with a carriage return (not a linefeed as you have written):

    wlen = write(fd, "READ\n", 5);

改为

    wlen = write(fd, "READ\r", 5);

如果它真的(它可能，但也可能不是)必须接收 cr lf:

Of if it really (it might, but maybe not) has to receive cr lf:

    wlen = write(fd, "READ\r\n", 6);

这篇关于在 Ubuntu 下从串口读取和写入 USB 规模的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！