Modbus protocol communication exception

One 、Modbus Protocol communication exception

• Address range
  • Slave address ：1-247： Valid address range 0： radio broadcast
• Data exception （ The data cannot be parsed normally ）
  • Large and small end storage problems
• Principle of exception handling （ Abnormal response ）

  • The slave will reply clearly

  • Function code high position 1
    Pictured ：
    

  • Meaning of abnormal information

    Code	name	meaning
    01	Illegal function	For servers ( Or slave station ) Come on , The function code received in the inquiry is not allowed . This may be because the function code is only applicable to new equipment and is not realizable in the selected unit . meanwhile , Also point out the server ( Or slave station ) Handle this request in an error state , for example ： Because it is not configured , And request to return the register value .
    02	Illegal data address	For servers ( Or slave station ) Come on , The data address received in the inquiry is not allowed . especially , The combination of reference number and transmission length is invalid . For with 100 For a register controller , With offset 96 And length 4 Your request will succeed , With offset 96 And length 5 The request of will generate an exception code 02.
    03	Illegal data value	For servers ( Or slave station ) Come on , The value included in the query is not allowed . This value indicates the failure in the remaining structure of the combined request , for example ： The implied length is incorrect . It doesn't mean that , because MODBUS The protocol does not know the significance of any special value of any special register , The data item submitted for storage in the register has a value beyond the expectation of the application .
    04	Slave station equipment failure	When the server ( Or slave station ) Trying to perform the requested operation , Produce errors that cannot be retrieved .
    05	confirm	Used with programming commands . The server ( Or slave station ) Request accepted , And cut is processing this request , But it takes a long time to do these operations . Return this response to prevent in the client ( Or master station ) Timeout error occurred in . The client ( Or master station ) You can continue to send the polling program completion message to determine whether the processing is completed .
    06	Slave device busy	Used with programming commands . The server ( Or slave station ) Processing long duration program commands . Zhang server ( Or slave station ) Idle , user ( Or master station ) The message should be retransmitted later .
    08	Store parity errors	And function code 20 and 21 And reference type 6 Use it together , Indicates that the extended file area cannot pass the consistency check . The server ( Or slave station ) Try to read the record file , But a parity error was found in the memory . The client ( Or the main party ) Can resend request , But it can be on the server ( Or slave station ) Service required on the equipment .
    0A	Unavailable gateway path	Use with gateway , Indicates that the gateway cannot assign an internal communication path from the input port to the output port for processing requests . It usually means that the gateway is misconfigured or overloaded .
    0B	Gateway target device response failed	Use with gateway , Indicates that no response was received from the target device . It usually means that the device is not in the network .

• The request frequency is abnormal
  • RTU Message request interval 3.5 Character time 1.5 Character time
• Message length limit
  • 0x07D0 Single request length of coil
  • 0x007D Length of register word request