Linux下的串行通信简介

计算机通常包括两个COM1和COM2两个串行通信接口(9针)

COM1和COM2在Linux上对应的设备是：

/dev/ttyS0和/dev/ttyS1

基本的流程：

打开串口资源，配置相应的参数，读写通信操作，关闭串口资源

下面以一个例子来学习一下串行通信

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>//进程控制函数库
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>//包含结构体termios，中最重要的是c_iflag
#include <errno.h>
int main()
{
    // open com ( com1=/dev/ttyS0 com2=/dev/ttyS1)
    int fd ;
    fd = open("/dev/ttyS0", O_RDWR) ; // open com1 in read and write mode

    if ( fd == -1)
    {
        perror("Open Com port error\n") ;
        exit(1) ;
    }
    // set com port attribute
    struct termios old_term ;// backup the old attribute of com
    struct termios new_term ;
    tcgetattr(fd, &old_term) ;//取得当前串口的值，并将其保存在old_term中    tcgetattr(fd, &new_term) ;

    cfsetispeed(&new_term, B19200) ;//设置输入和输出波特率
    cfsetospeed(&new_term, B19200) ;//这一句好像是为了有的位段不用设置

     //控制模式

    new_term.c_cflag &= ~CSIZE ;

    int data_bit = 7 ;
    if (data_bit == 7)
    {
        new_term.c_cflag |= CS7 ;    // 7-bit data
    }
    else
    {    
        new_term.c_cflag |= CS8 ;    // 8-bit data
    }

    // set parity

    int parity = "N" ; // N, E, O, S


    switch(parity)
    {
    case 'n':
    case 'N':
        // no parity

        new_term.c_cflag &= ~PARENB ;
        new_term.c_iflag &= ~INPCK ;
        break ;
    case 'O':
    case 'o':
        // ji "O"

        new_term.c_cflag |= (PARODD | PARENB) ;
        new_term.c_iflag |= INPCK ;
        break ;
    case 'E':
    case 'e':
        // odd "E"

        new_term.c_cflag |= PARENB ;
        new_term.c_cflag &= ~PARODD ;
        new_term.c_iflag |= INPCK ;
        break ;
    case 'S':
    case 's':
        // "S"

        new_term.c_cflag &= ~PARENB ;
        new_term.c_cflag &= CSTOPB ;
        new_term.c_iflag |= INPCK ;
        break ;
    }// switch(parity)


    // set stop bit

    int stop_bit = 1 ;    // 1, 2

    switch(stop_bit)
    {
    case 1:
        new_term.c_cflag &= ~CSTOPB ;    
        break ;
    case 2:
        new_term.c_cflag |= CSTOPB ;
        break ;
    }
    tcsetattr(fd, TCSANOW, &new_term) ;//设置当前的串口的参数为new_term
    tcflush(fd, TCIOFLUSH) ;//清空所有队列在串口上的输入输出
   
    // write data
    char buffer[1024] ;
    int times = 0 ;
    while (times++ < 10 )
    {    
        strcpy(buffer, "hello, world!") ;
        int length = strlen(buffer) ;
        int nWriteBytes ;
        nWriteBytes = write(fd, buffer, length) ;    
        printf("write com data len=%d\n", nWriteBytes) ;
    }

    tcsetattr(fd, TCSANOW, &old_term) ;//恢复原有的默认的设置

    close(fd) ;
}