当然可以帮您提供一个简单的C语言MODBUS程序示例。以下是一个基本的MODBUS RTU通信读取保持寄存器的示例:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#define SERIAL_PORT "/dev/ttyUSB0" // 串口设备路径
// MODBUS函数码
#define MODBUS_READ_HOLDING_REGISTERS 0x03
// MODBUS帧结构体
typedef struct {
uint8_t slaveAddress; // 从机地址
uint8_t functionCode; // 功能码
uint16_t startAddress; // 起始地址
uint16_t quantity; // 寄存器数量
uint8_t crcLowByte; // CRC校验低字节
uint8_t crcHighByte; // CRC校验高字节
} ModbusFrame;
// 计算CRC校验值
uint16_t calculateCRC(uint8_t *data, size_t length) {
uint16_t crc = 0xFFFF;
for (size_t i = 0; i < length; i++) {
crc ^= data[i];
for (int j = 0; j < 8; j++) {
if (crc & 1) {
crc >>= 1;
crc ^= 0xA001;
} else {
crc >>= 1;
}
}
}
return crc;
}
// 发送MODBUS请求并接收响应
int sendModbusRequest(int fd, ModbusFrame request, uint16_t *response) {
// 发送请求
write(fd, &request, sizeof(ModbusFrame));
// 读取响应
ModbusFrame receivedFrame;
ssize_t bytesRead = read(fd, &receivedFrame, sizeof(ModbusFrame));
// 验证CRC校验
uint16_t calculatedCRC = calculateCRC((uint8_t*)&receivedFrame, bytesRead - 2);
uint16_t receivedCRC = (receivedFrame.crcHighByte << 8) | receivedFrame.crcLowByte;
if (bytesRead != sizeof(ModbusFrame) || calculatedCRC != receivedCRC) {
printf("MODBUS response error\n");
return -1;
}
// 解析响应数据
*response = (receivedFrame.crcLowByte << 8) | receivedFrame.crcHighByte;
return 0;
}
int main() {
int fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY);
if (fd < 0) {
perror("Failed to open serial port");
return -1;
}
struct termios serialConfig;
memset(&serialConfig, 0, sizeof(struct termios));
// 设置波特率为9600,8位数据位,无奇偶校验,1个停止位
serialConfig.c_cflag = B9600 | CS8 | CLOCAL | CREAD;
tcflush(fd, TCIFLUSH);
tcsetattr(fd, TCSANOW, &serialConfig);
// 构建MODBUS请求帧
ModbusFrame request;
request.slaveAddress = 1; // 从机地址
request.functionCode = MODBUS_READ_HOLDING_REGISTERS; // 功能码为读取保持寄存器
request.startAddress = 0; // 起始地址为0
request.quantity = 2; // 需要读取的寄存器数量
// 计算CRC校验值并填充到请求帧中
uint16_t crc = calculateCRC((uint8_t*)&request, sizeof(ModbusFrame) - 4);
request.crcLowByte = crc & 0xFF;
request.crcHighByte = (crc >> 8) & 0xFF;
// 发送请求并接收响应
uint16_t response[2];
if (sendModbusRequest(fd, request, response) == 0) {
printf("Response: %d %d\n", response[0], response[1]);
}
close(fd);
return 0;
}
请注意,以上示例只是一个基本的MODBUS RTU通信读取保持寄存器的示例,并且需要根据您的具体硬件配置和需求进行相应修改。此外,还需要根据实际情况进行错误处理和其他功能的实现。
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