I-7242D user manual
I-7242D DeviceNet/Modbus RTU Gateway User’s Manual, July 2006, Version 1.1 112/124
8.7 Exception Responses
When a slave receives the query without a communication error, but
cannot handle it, the slave will return an exception response informing the
master of the nature of the error. The structure of an exception response is
independent of the Modbus command associated with the “Function” field of
the query involved. The whole frame of an exception response is shown below.
Slave Address
Modbus address (1 to 247). The value of this field is identical to that of the
“Slave Address” field of the query involved.
Function
The value of this field is set to 0x80 + the value of the “Function” field of
the query involved.
Exception Code
Code indicating the nature of the error which has caused the exception
response
Checksum (Lo)
Checksum (Hi)
Error check
Code Name Meaning
0x01 Illegal Function
The function code received in the query
is not an allowable action for
the slave.
0x02
Illegal Data
Address
The data address received in the query is not an allowable address for the
slave.
0x03
Illegal Data
Value
A value contained in the query data field is not an allowable value for the
slave.
0x04
Slave Device
Failure
An unrecoverable error occurred while the slave was attempting to perform
the requested action.
0x05 Acknowledge
The slave has accepted the request and is processing it, but a long
duration of time will be required to do so.
The gateway should transmit
subsequent queries in order to determine whether the request has
finished or not.
0x06
Slave Device
Busy
The slave is engaged in processing a long–duration program command.
So the gateway should re-transmit the query subsequently.
0x07
Negative
Acknowledge
The slave cannot perform the program function received in the query.
This
exception only affects commands 0x0D and 0x0E.
0x08
Memory Parity
Error
The slave attempted to read extended memory, but detected a parity error
in the memory.
This exception only affects standard commands 0x14
and 0x15.