Archived: What Do the Various Modbus Exception Codes in Lookout Mean?

Solution

Modbus Exception Codes
Exception Code Number	Code	Description
01	Illegal Function	The function code received in the query is not an allowable action for the slave. If a Poll Program Complete command was issued, this code indicates that no program function preceded it.
02	Illegal Data Address	The data address received in the query is not an allowable address for the slave
03	Illegal Data Value	A value contained in the query data field is not an allowable value for the slave
04	Slave Device Failure	An unrecoverable error occured while the slave was attempting to perform the requested action
05	Acknowledge	The slave has accepted the request and is processing it, but a long duration of time will be required to do so. This response is returned to prevent a timeout error from occurring in the master. The master can next issue a Poll Program Complete message to determine if processing is completed
06	Slave Device Busy	The slave is engaged in processing a long-duration program command. The master should retransmit the message later when the slave is free.
07	Negative Acknowledge	The slave cannot perform the program function received in the query. This code is returned for an unsuccessful programming request using function code 13 or 14 decimal. The master should request diagnostic or error information from the slave
08	Memory Parity Error	The slave attempted to read extended memory, but detected a parity error in the memory. The master can retry the request, but service may be required on the slave device