python
# 线圈操作
READ_COILS = 0x01                    # 读线圈
WRITE_SINGLE_COIL = 0x05            # 写单个线圈
WRITE_MULTIPLE_COILS = 0x0F         # 写多个线圈

# 离散输入
READ_DISCRETE_INPUTS = 0x02         # 读离散输入

# 寄存器操作
READ_INPUT_REGISTER = 0x04          # 读输入寄存器
READ_HOLDING_REGISTERS = 0x03       # 读保持寄存器
WRITE_SINGLE_REGISTER = 0x06        # 写单个寄存器
WRITE_MULTIPLE_REGISTERS = 0x10     # 写多个寄存器

python
READ_WRITE_MULTIPLE_REGISTERS = 0x17  # 读写多个寄存器
MASK_WRITE_REGISTER = 0x16           # 屏蔽写寄存器
READ_FIFO_QUEUE = 0x18               # 读FIFO队列
READ_FILE_RECORD = 0x14              # 读文件记录
WRITE_FILE_RECORD = 0x15             # 写文件记录

python
READ_EXCEPTION_STATUS = 0x07         # 读取异常状态
DIAGNOSTICS = 0x08                   # 诊断
GET_COM_EVENT_COUNTER = 0x0B         # 获取通信事件计数
GET_COM_EVENT_LOG = 0x0C             # 获取通信事件日志
REPORT_SERVER_ID = 0x11              # 报告服务器ID
READ_DEVICE_IDENTIFICATION = 0x2B     # 读取设备标识

python
ILLEGAL_FUNCTION = 0x01              # 非法功能
ILLEGAL_DATA_ADDRESS = 0x02          # 非法数据地址
ILLEGAL_DATA_VALUE = 0x03            # 非法数据值
SERVER_DEVICE_FAILURE = 0x04         # 服务器设备故障

python
ACKNOWLEDGE = 0x05                   # 确认
SERVER_DEVICE_BUSY = 0x06            # 服务器设备忙
MEMORY_PARITY_ERROR = 0x08          # 内存奇偶校验错误
GATEWAY_PATH_UNAVAILABLE = 0x0A      # 网关路径不可用
DEVICE_FAILED_TO_RESPOND = 0x0B      # 设备响应失败

python
CRC_LENGTH = 0x02                    # CRC长度
ERROR_BIAS = 0x80                    # 错误偏移
RESPONSE_HDR_LENGTH = 0x02           # 响应头长度
ERROR_RESP_LEN = 0x05               # 错误响应长度
FIXED_RESP_LEN = 0x08               # 固定响应长度
MBAP_HDR_LENGTH = 0x07              # MBAP头长度

python
def generate_crc16_table():
    """生成CRC16查找表的算法"""
    crc_table = []
    for byte in range(256):
        crc = 0x0000
        for _ in range(8):
            if (byte ^ crc) & 0x0001:
                crc = (crc >> 1) ^ 0xa001
            else:
                crc >>= 1
            byte >>= 1
        crc_table.append(crc)
    return crc_table

python
# 读取线圈
function_code = READ_COILS
# 写入单个寄存器
function_code = WRITE_SINGLE_REGISTER

python
def check_response(response):
    if response[1] & ERROR_BIAS:
        error_code = response[2]
        if error_code == ILLEGAL_FUNCTION:
            raise ValueError("非法功能码")
        elif error_code == ILLEGAL_DATA_ADDRESS:
            raise ValueError("非法数据地址")

python
def calculate_crc(message):
    """计算消息的CRC值"""
    crc = 0xFFFF
    for byte in message:
        crc = (crc >> 8) ^ CRC16_TABLE[(crc ^ byte) & 0xFF]
    return crc