沁恒ch573 modbus例程

以下是使用沁恒ch573芯片实现Modbus协议的例程：

#include "ch573.h"
#include "uart.h"

#define MODBUS_ADDR  1

#define MODBUS_READ_HOLDING_REGISTERS  0x03

typedef struct 
{
    uint8_t addr;
    uint8_t func_code;
    uint16_t start_addr;
    uint16_t quantity;
    uint8_t crc_lo;
    uint8_t crc_hi;
} modbus_request_t;

typedef struct 
{
    uint8_t addr;
    uint8_t func_code;
    uint8_t byte_count;
    uint16_t data[20];
    uint8_t crc_lo;
    uint8_t crc_hi;
} modbus_response_t;

void modbus_handler(uint8_t* buf, uint16_t len)
{
    modbus_request_t* req = (modbus_request_t*)buf;
    if(req->addr == MODBUS_ADDR)
    {
        modbus_response_t res;
        res.addr = MODBUS_ADDR;
        res.func_code = req->func_code;
        res.byte_count = req->quantity * 2;
        for(int i=0;i<req->quantity;i++)
        {
            res.data[i] = 100 + req->start_addr + i; // 模拟读取寄存器的值
        }
        uint16_t crc = crc16_modbus((uint8_t*)&res, sizeof(res) - 2);
        res.crc_lo = crc & 0xff;
        res.crc_hi = crc >> 8;
        uart_send((uint8_t*)&res, sizeof(res));
    }
}

int main()
{
    ch573_init();
    uart_init();
    while(1)
    {
        uint8_t buf[256];
        uint16_t len = uart_recv(buf, 256);
        if(len > 0)
        {
            modbus_handler(buf, len);
        }
    }
    return 0;
}

该例程实现了Modbus协议的主要功能，即读取保持寄存器的值。在`modbus_handler`函数中，根据收到的请求，返回对应的响应。其中`crc16_modbus`函数是计算Modbus协议CRC校验码的函数。