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What Do The Modbus Exception Codes Reported In The Event Log Mean?


Last Update: 11/7/2018

Modbus Exception Codes are returned by the Modbus device or the Modbus Gateway. For an explanation of the Modbus Exception Codes reported in the Modbus Suite of drivers, refer to the list below. For more information, refer to the Modbus Application Protocol manual at modbus.org.>

  • Exception Code 01: The function code received in the query is not an allowable action for the server (or slave). This may be because the function code only applies to newer devices or was not implemented in the selected unit. It could also indicate that the server (or slave) is in the wrong state to process a request of this type (such as because it is not configured and is being asked to return register values).
  • Exception Code 02: The data address received in the query is not an allowable address for the server (or slave). More specifically, the combination of reference number and transfer length is invalid. For a controller with 100 registers, a request with offset 96 and length 4 would succeed, whereas a request with offset 96 and length 5 would generate Exception Code 02. When the server receives this exception code, it will deactivate the tag or tags involved in the response by default. To change the default action to invalidate the tags for one poll cycle, open Device Properties | Error Handling and then uncheck Deactivate tags on illegal address exception parameter.
  • Exception Code 03: A value contained in the Query data field is not allowed for the server (or slave). This indicates a fault in the structure of the complex request (such as an incorrect implied length). It does not mean that a data item that was submitted for storage in a register has a value outside of the application program's expectations. The Modbus protocol is unaware of the significance of any particular value of any particular register. When the server receives this exception code, it will deactivate the tags involved in the response by default. To invalidate the tags for one poll cycle, click Device Properties | Error Handling. Then, uncheck Deactivate tags on illegal address exception parameter.
  • Exception Code 04: A value contained in the Query data field is not allowed for the server (or slave). This indicates a fault in the structure of the complex request (such as an incorrect implied length). It does not mean that a data item that was submitted for storage in a register has a value outside of the application program's expectations. The Modbus protocol is unaware of the significance of any particular value of any particular register. When the server receives this exception code, it will deactivate the tags involved in the response by default. To invalidate the tags for one poll cycle, click Device Properties | Error Handling. Then, uncheck Deactivate tags on illegal address exception parameter.
  • Exception Code 05: Although the slave has accepted the request and is processing it, a long amount of time is required to do so. This response prevents a timeout error from occurring in the master. The master can then issue a Poll Program Complete message to determine whether processing has completed.
  • Exception Code 06: The slave is processing a long-duration program command. The master should retransmit the message later when the slave is free.
  • Exception Code 07: The slave cannot perform the program function received in the query. This code will be returned for an unsuccessful programming request using Function Code 13 or 14 decimal. The master should request diagnostic or error information from the slave.
  • Exception Code 08: While attempting to read extended memory, the slave detected a parity error in the memory. Although the master can retry the request, service may be required on the slave device.
  • Exception Code 10: Specialized use in conjunction with gateways indicates that the gateway was unable to allocate an internal communication path from the input port to the output port for processing the request. This usually means that the gateway is misconfigured or overloaded.
  • Exception Code 11: Specialized use in conjunction with gateways indicates that no response was obtained from the target device. This usually means that the device is not present on the network.
  • Exception Code 111: The function code received in the query is not an allowable action for the server or slave. This may be because the function code only applies to newer devices, and was not implemented in the selected unit. It could also indicate that the server or slave is in the wrong state to process a request of this type (such as, it is being asked to return register values but is not configured). This error is specifically returned by the Hilscher Modbus Plus CIF card.
  • Exception Code 114: An unrecoverable error occurred while the server or slave was attempting to perform the requested action. This error is specifically returned by the Hilscher Modbus Plus CIF card.
Related Protocols
Modbus Ethernet Modbus Plus