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1.概述
RS485是一种串行通信标准，广泛应用于工业控制、自动化系统、建筑物自动化和数据采集等领域。它的名称"RS485"代表"Recommended Standard 485"，这个标准定义了一种物理层通信协议，旨在克服早期串行通信标准的一些限制。 RS485协议的主要特点之一是它使用差分信号传输数据。这意味着它同时传输正极性信号和负极性信号，从而降低了外部电磁干扰对通信的影响。这使得RS485非常适合于噪声较高的工业环境，以及需要长距离通信的应用。RS485支持半双工或全双工通信模式，允许设备在发送和接收数据之间切换，或同时进行双向通信。 另一个RS485的关键特点是多点通信。多个设备可以连接到同一RS485总线上，每个设备都有一个唯一的地址。当一个设备发送数据时，其他设备可以选择是否接收该数据，从而实现了多点到多点的通信。这种特性使RS485成为分布式控制系统的理想选择，例如工业自动化中的传感器、PLC、仪表和计算机等设备可以通过RS485进行通信
2.硬件连接
如下所示为板子的外设接口示意图，引出了RS485引脚，通过USB转RS485与电脑连接。
电路硬件设计，使用的是UART7作为RS485的接口，对应是PE8和PE10，如下所示：
3.软件设计
#include<stdio.h> #include<termios.h> #include<linux/ioctl.h> #include<linux/serial.h> #include<asm-generic/ioctls.h> /* TIOCGRS485 + TIOCSRS485 ioctl definitions */ #include<unistd.h> #include<errno.h> #include<fcntl.h> #include<sys/types.h> #include<sys/stat.h> #include<string.h> #include<stdlib.h> #include<getopt.h> typedef enum { DISABLE = 0, ENABLE }RS485_ENABLE_t; int set_port(intfd, int nSpeed, int nBits, char nEvent, int nStop) { struct termios newtio, oldtio; memset(&oldtio, 0, sizeof(oldtio)); /* save the old serial port configuration*/ if (tcgetattr(fd, &oldtio) != 0) { perror("set_port/tcgetattr"); return -1; } memset(&newtio, 0, sizeof(newtio)); /* ignore modem control lines and enablereceiver */ newtio.c_cflag = newtio.c_cflag |= CLOCAL| CREAD; newtio.c_cflag &= ~CSIZE; /* set character size */ switch (nBits) { case 8: newtio.c_cflag |= CS8; break; case 7: newtio.c_cflag |= CS7; break; case 6: newtio.c_cflag |= CS6; break; case 5: newtio.c_cflag |= CS5; break; default: newtio.c_cflag |= CS8; break; } /* set the parity */ switch (nEvent) { case 'o': case 'O': newtio.c_cflag |= PARENB; newtio.c_cflag |= PARODD; newtio.c_iflag |= (INPCK | ISTRIP); break; case 'e': case 'E': newtio.c_cflag |= PARENB; newtio.c_cflag &= ~PARODD; newtio.c_iflag |= (INPCK | ISTRIP); break; case 'n': case 'N': newtio.c_cflag &= ~PARENB; break; default: newtio.c_cflag &= ~PARENB; break; } /* set the stop bits */ switch (nStop) { case 1: newtio.c_cflag &= ~CSTOPB; break; case 2: newtio.c_cflag |= CSTOPB; break; default: newtio.c_cflag &= ~CSTOPB; break; } /* set output and input baud rate */ switch (nSpeed) { case 0: cfsetospeed(&newtio, B0); cfsetispeed(&newtio, B0); break; case 50: cfsetospeed(&newtio, B50); cfsetispeed(&newtio, B50); break; case 75: cfsetospeed(&newtio, B75); cfsetispeed(&newtio, B75); break; case 110: cfsetospeed(&newtio, B110); cfsetispeed(&newtio, B110); break; case 134: cfsetospeed(&newtio, B134); cfsetispeed(&newtio, B134); break; case 150: cfsetospeed(&newtio, B150); cfsetispeed(&newtio, B150); break; case 200: cfsetospeed(&newtio, B200); cfsetispeed(&newtio, B200); break; case 300: cfsetospeed(&newtio, B300); cfsetispeed(&newtio, B300); break; case 600: cfsetospeed(&newtio, B600); cfsetispeed(&newtio, B600); break; case 1200: cfsetospeed(&newtio, B1200); cfsetispeed(&newtio, B1200); break; case 1800: cfsetospeed(&newtio, B1800); cfsetispeed(&newtio, B1800); break; case 2400: cfsetospeed(&newtio, B2400); cfsetispeed(&newtio, B2400); break; case 4800: cfsetospeed(&newtio, B4800); cfsetispeed(&newtio, B4800); break; case 9600: cfsetospeed(&newtio, B9600); cfsetispeed(&newtio, B9600); break; case 19200: cfsetospeed(&newtio, B19200); cfsetispeed(&newtio, B19200); break; case 38400: cfsetospeed(&newtio, B38400); cfsetispeed(&newtio, B38400); break; case 57600: cfsetospeed(&newtio, B57600); cfsetispeed(&newtio, B57600); break; case 115200: cfsetospeed(&newtio, B115200); cfsetispeed(&newtio, B115200); break; case 230400: cfsetospeed(&newtio, B230400); cfsetispeed(&newtio, B230400); break; default: cfsetospeed(&newtio, B115200); cfsetispeed(&newtio, B115200); break; } /* set timeout in deciseconds for non-canonicalread */ newtio.c_cc[VTIME] = 0; /* set minimum number of characters fornon-canonical read */ newtio.c_cc[VMIN] = 0; /* flushes data received but not read */ tcflush(fd, TCIFLUSH); /* set the parameters associated with theterminal from thetermios structure and the change occurs immediately */ if ((tcsetattr(fd, TCSANOW, &newtio))!= 0) { perror("set_port/tcsetattr"); return -1; } return 0; } /** * @brief: open serial port * @Param: dir: serial device path */ intopen_port(char *dir) { int fd; fd = open(dir, O_RDWR); if (fd < 0) { perror("open_port"); } return fd; }
void print_usage(FILE*stream, int exit_code) { fprintf(stream, "Usage: option [dev... ] \n"); fprintf(stream, "\t-h --help Display this usage information.\n" "\t-d --device The device ttyS[0-3] or ttySCMA[0-1]\n" "\t-b --baudrate Set the baud rate you canselect\n" "\t [230400, 115200, 57600, 38400,19200, 9600, 4800, 2400, 1200, 300]\n" "\t-s --string Write the device data\n" "\t-e --1 or 0 Write 1 to enable the rs485_mode(only at atmel)\n"); exit(exit_code); } /* PC6 forenable*/ voidrs485_enable_ya157c(void) { system("echo 377 >sys/class/gpio/export"); system("echo out >/sys/class/gpio/P2_1/direction"); system("echo 1 >/sys/class/gpio/P2_1/value"); } intrs485_enable(const int fd, const RS485_ENABLE_t enable) { struct serial_rs485 rs485conf; int res; /* Get configure from device */ res = ioctl(fd, TIOCGRS485,&rs485conf); if (res < 0) { perror("Ioctl error on getting485 configure:"); close(fd); return res; } /* Set enable/disable to configure */ if (enable) { // Enable rs485 mode rs485conf.flags |=SER_RS485_ENABLED; } else { // Disable rs485 mode rs485conf.flags &=~(SER_RS485_ENABLED); } rs485conf.delay_rts_before_send =0x00000004; /* Set configure to device */ res = ioctl(fd, TIOCSRS485,&rs485conf); if (res < 0) { perror("Ioctl error on setting485 configure:"); close(fd); } return res; } intchange_bit_rs485(int fd, int value) { struct serial_rs485 rs485conf; int res; /* Get configure from device */ res = ioctl(fd, TIOCGRS485,&rs485conf); if (res < 0) { perror("Ioctl error on getting485 configure:"); close(fd); return res; } /*rs485 send - recv*/ if (value == 1) rs485conf.flags |=SER_RS485_RTS_AFTER_SEND; else if (value == 0) rs485conf.flags &=~SER_RS485_RTS_AFTER_SEND; else ; /* Set configure to device */ res = ioctl(fd, TIOCSRS485,&rs485conf); if (res < 0) { perror("Ioctl error on setting485 configure:"); close(fd); } return res; } int main(intargc, char *argv[]) { char *write_buf = "MYiR UARTTEST"; char read_buf[100]; int fd, i, len, nread, r; pid_t pid; int next_option; struct termios oldtio; int speed; char *device; int spee_flag = 0, device_flag = 0; const char *const short_options ="hd:s:b:e:"; unsigned int ffl_cnt = 0; const struct option long_options[] = { {"help", 0, NULL, 'h'}, {"device", 1, NULL, 'd'}, {"string", 1, NULL, 's'}, {"baudrate", 1, NULL,'b'}, {NULL, 0, NULL, 0}}; if (argc < 2) { print_usage(stdout, 0); exit(0); } while (1) { next_option = getopt_long(argc,argv, short_options, long_options, NULL); if (next_option < 0) break; switch (next_option) { case 'h': print_usage(stdout, 0); break; case 'd': device = optarg; device_flag = 1; break; case 'b': speed = atoi(optarg); spee_flag = 1; break; case 's': write_buf = optarg; break; case 'e': r = atoi(optarg); break; case '?': print_usage(stderr, 1); break; default: abort(); } } if ((!device_flag) || (!spee_flag)) { print_usage(stderr, 1); exit(0); } /* open serial port */ fd = open_port(device); if (fd < 0) { perror("open failed"); return -1; } if (r) { rs485_enable_ya157c(); // rs485_enable(fd,ENABLE); } /* set serial port */ i = set_port(fd, speed, 8, 'N', 1); if (i < 0) { perror("set_portfailed"); return -1; } // send 4 write(fd, write_buf, strlen(write_buf)); write(fd, write_buf, strlen(write_buf)); write(fd, write_buf, strlen(write_buf)); write(fd, write_buf, strlen(write_buf)); usleep(40000); // 40ms change_bit_rs485(fd, 0); // recv mode // usleep(500000); while (1) { nread = read(fd, read_buf,sizeof(read_buf)); if (nread > 0) { printf("RECV[%3d]:", nread); for (i = 0; i < nread;i++) printf("0x%02x", read_buf); printf("\n"); // send write(fd, write_buf,strlen(write_buf)); usleep(40000); // 40ms change_bit_rs485(fd, 0); //recv mode } usleep(1000); } /* restore the old configuration */ tcsetattr(fd, TCSANOW, &oldtio); close(fd); return 0; }
4.通信测试
电脑使用上位机通过USB转RS485与开发板通信，通信配置与开发板配置保持一致。
开发板RS485参数配置如下所示： 通过上位机发送的数据，开发板将上位机发送的数据打印出来，如下所示：数据接收正确
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发表于 2023-9-29 18:13:14
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