modbus

Modbus Exception Codes

Exception codes returned by a Modbus server in an exception response when it cannot fulfil a client request. Defined in the Modbus Application Protocol Specification V1.1b3, section 7.

10 codes

references modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf

· All codes 10 codes

1 ILLEGAL_FUNCTION The function code in the request is not recognised or is not allowed by the server. This may indicate the server has not implemented the requested function, or is not in a state that allows it.
2 ILLEGAL_DATA_ADDRESS The data address referenced in the request is not available on the server. This typically means the combination of reference number and transfer length is invalid.
3 ILLEGAL_DATA_VALUE A value contained in the request data field is not acceptable to the server. This indicates a fault in the structure of the request, not the value of the data itself.
4 SERVER_DEVICE_FAILURE An unrecoverable error occurred while the server was attempting to perform the requested action. This is a generic server fault with no more specific cause available.
5 ACKNOWLEDGE The server has accepted the request and is processing it, but the processing will take too long to return a normal response. Returned to prevent a timeout on the client; the client should poll for completion using function code 11 (0x0B).
6 SERVER_DEVICE_BUSY The server is busy processing a long-duration command and cannot accept a new request at this time. The client should retry the request when the server is free.
7 NEGATIVE_ACKNOWLEDGE The server cannot perform the program function received in the request. Used alongside a programming command when the server cannot fulfil the request; the client should retrieve the error condition from the server using a get program complete routine.
8 MEMORY_PARITY_ERROR The server detected a parity error in the memory when attempting to read extended memory or record file. The client may retry the request; however the parity error will likely persist until the device is serviced.
10 GATEWAY_PATH_UNAVAILABLE The gateway was unable to allocate an internal communication path to process the request. This typically indicates the gateway is misconfigured or overloaded.
11 GATEWAY_TARGET_DEVICE_FAILED_TO_RESPOND The gateway failed to obtain a response from the target device. This usually indicates that the target device is not present on the network.