单片机modbus从机程序

以下是基于STM32单片机的Modbus从机程序示例：

#include "modbus.h"

/* Modbus function codes */
#define READ_COILS                      0x01
#define READ_DISCRETE_INPUTS            0x02
#define READ_HOLDING_REGISTERS          0x03
#define READ_INPUT_REGISTERS            0x04
#define WRITE_SINGLE_COIL               0x05
#define WRITE_SINGLE_REGISTER           0x06
#define WRITE_MULTIPLE_COILS            0x0F
#define WRITE_MULTIPLE_REGISTERS        0x10

/* Modbus frame structure */
typedef struct {
    uint8_t address;
    uint8_t function_code;
    uint8_t data[MODBUS_MAX_DATA_SIZE];
    uint16_t data_size;
    uint16_t crc;
} modbus_frame_t;

/* Modbus handler function */
void modbus_handler(uint8_t* rx_buffer, uint16_t rx_size, uint8_t* tx_buffer, uint16_t* tx_size) {
    modbus_frame_t frame;
    uint16_t crc;

    /* Check the received frame for errors */
    if (modbus_check_frame(rx_buffer, rx_size, &frame)) {
        /* Process the modbus function based on the function code */
        switch (frame.function_code) {
            case READ_COILS:
                /* Process read coils function */
                break;
            case READ_DISCRETE_INPUTS:
                /* Process read discrete inputs function */
                break;
            case READ_HOLDING_REGISTERS:
                /* Process read holding registers function */
                break;
            case READ_INPUT_REGISTERS:
                /* Process read input registers function */
                break;
            case WRITE_SINGLE_COIL:
                /* Process write single coil function */
                break;
            case WRITE_SINGLE_REGISTER:
                /* Process write single register function */
                break;
            case WRITE_MULTIPLE_COILS:
                /* Process write multiple coils function */
                break;
            case WRITE_MULTIPLE_REGISTERS:
                /* Process write multiple registers function */
                break;
            default:
                /* Invalid function code */
                break;
        }

        /* Construct the response frame */
        frame.address = MODBUS_ADDRESS;
        frame.function_code += 0x80;
        crc = modbus_calculate_crc((uint8_t*)&frame, frame.data_size + 2);
        frame.crc = (crc << 8) | (crc >> 8);

        /* Copy the response frame to the transmit buffer */
        *tx_size = modbus_build_frame(tx_buffer, &frame);
    }
}

该程序使用了modbus.h头文件中定义的函数进行Modbus通信处理。在处理Modbus帧时，程序首先对接收到的帧进行错误检查，然后根据帧的功能码进行相应的处理。最后，程序构建响应帧并将其复制到传输缓冲区以进行发送。

需要注意的是，该程序仅提供了Modbus通信处理的基本框架，具体的Modbus功能需要根据实际需求进行实现。