关于rs422的串口通信问题

debianl

在项目开发中，有一个外设是rs232转rs422的接口，这是客户方很早以前购买的，没有文档，只有一个windows的源程序库，看了一下大概流程是这样的：先将串口设置为波特率9600、8个数据位、Mark Parity、1个停止位，发送地址信息，然后再将奇偶校验调整为Space Parity发送请求数据，最后读取返回的数据。可是我在linux下一直未成功，返回的数据总是错误的，下面我帖出我在windows上写的测试程序和linux下的测试程序，希望有做过rs422串口通信开发的兄弟给点建议。(windows测试程序的返回结果是正确的，正确结果应为5个字节，而且每次都相同，linux下有时候不返回数据有时候返回4个字节，而且这个4个字节经常变化)

linux下的测试代码：

1. #include <stdio.h>
2. #include <unistd.h>
3. #include <stdlib.h>
4. #include <sys/types.h>
5. #include <sys/stat.h>
6. #include <fcntl.h>
7. #include <termios.h>
8. #include <string.h>
10. int
11. main(int argc, char **argv)
12. {
13.   if (argc != 2) {
14.     printf("Usage: %s <comdev>\n", argv[0]);
15.     return -1;
16.   }
18.   int fd = open(argv[1], O_RDWR | O_NOCTTY);
19.   if (fd == -1) {
20.     printf("Initialize COM device failed.\n");
21.     return -1;
22.   }
24.   struct termios options;
26.   tcgetattr(fd, &options);
27.   cfmakeraw(&options);
28.   options.c_cflag &= ~CSIZE;
29.   options.c_cflag |= CRTSCTS;
30.   options.c_cflag |= CMSPAR;
31.   options.c_cflag |= PARODD;
32.   options.c_cflag |= PARENB;
33.   options.c_cflag |= CS8;
34.   options.c_cflag &= ~CSTOPB;
35.   options.c_iflag |= IGNPAR | IGNBRK | INPCK;
36.   options.c_cc[VTIME] = 100;
37.   options.c_cc[VMIN] = 0;
38.   cfsetispeed(&options, B9600);
39.   cfsetospeed(&options, B9600);
40.   tcflush(fd, TCIOFLUSH);
41.   tcsetattr(fd, TCSANOW, &options);
43.   char addr = 0x01;
44.   if (write(fd, &addr, 1) == -1)
45.     goto failed;
47.   usleep(1000);
49.   options.c_cflag &= ~PARODD;
50.   tcsetattr(fd, TCSADRAIN, &options);
52.   usleep(1000);
54.   unsigned char buf[10];
55.   memcpy(buf, "\x02\x85\x83\x04", 4);
57.   if (write(fd, buf, 4) == -1)
58.     goto failed;
60.   usleep(1000);
62.   ssize_t read_n;
63.   int i;
64.   read_n = read(fd, buf, sizeof(buf));
65.   printf("result: %d\n", read_n);
66.   for (i = 0; i < read_n; ++i)
67.     printf("%02X ", buf[i]);
68.   printf("\n");
70.   close(fd);
71.   return 0;
73. failed:
74.   close(fd);
75.   return -1;
76. }

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windows下的测试代码：

1. #include <windows.h>
2. #include <stdio.h>
3. #include <stdlib.h>
4. #include <string.h>
6. int
7. main(int argc, char **argv)
8. {
9.         HANDLE h_com;
10.         unsigned char addr = 0x01;
11.         unsigned char buf[10];
12.         int i;
13.         DCB dcb;
14.         COMMTIMEOUTS timeouts;
15.         DWORD n;
17.         if (argc != 2) {
18.                 printf("%s <comdev>\n", argv[0]);
19.                 return -1;
20.         }
22.         h_com = CreateFile(argv[1], GENERIC_READ | GENERIC_WRITE,
23.                 0, NULL, OPEN_EXISTING, 0, NULL);
24.         if (h_com == INVALID_HANDLE_VALUE) {
25.                 printf("Initialize COM device failed\n");
26.                 return -1;
27.         }
29.         GetCommState(h_com, &dcb);
30.         dcb.BaudRate = 9600;
31.         dcb.ByteSize = 8;
32.         dcb.Parity = MARKPARITY;
33.         dcb.StopBits = ONESTOPBIT;
34.         SetCommState(h_com, &dcb);
36.         GetCommTimeouts(h_com, &timeouts);
37.         timeouts.ReadTotalTimeoutConstant = 10;
38.         SetCommTimeouts(h_com, &timeouts);
40.         WriteFile(h_com, &addr, sizeof(addr), &n, NULL);
42.         Sleep(1);
43.         dcb.Parity = SPACEPARITY;
44.         SetCommState(h_com, &dcb);
45.         memcpy(buf, "\x02\x85\x83\04", 4);
46.         WriteFile(h_com, buf, 4, &n, NULL);
48.         Sleep(1);
49.         ReadFile(h_com, buf, sizeof(buf), &n, NULL);
50.         printf("read %d bytes\n", n);
52.         for (i = 0; i < n; ++i)
53.                 printf("%02x ", buf[i]);
54.         printf("\n");
56.         return 0;
57. }

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