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13. Appendix F: Modbus Commands
Code
Name of the
exception
Description of the exception
16#01 ILLEGAL FUNCTION The query’s “Function” command code is not implemented in the Modbus slave
software, or it is unable to process it for the moment.
16#02 ILLEGAL DATA
ADDRESS
The combination of the query’s “Starting Address” and “No. of Registers” fields
(or assimilated fields) gives access to one or more addresses which are not
accessible on the Modbus slave.
16#03
I
LLEGAL DATA
VALUE
The value of one of the Modbus query’s fields is outside the authorized limits.
This error does not affect the content of the “Data” (or assimilated) fields, as this
error only takes account of the fields used for managing the Modbus protocol.
16#04 SLAVE DEVICE
FAILURE
An unrecoverable failure has occurred when processin the command.
16#05
(1)
ACKNOWLEDGE The Modbus slave informs the gateway that it has accepted the command
(acknowledgement), but that it will take too long to process it and it cannot afford
to wait for the completion of this process before sending a response.
The gateway should transmit subsequent queries in order to determine whether
the command has finished or not.
16#06
(1)
SLAVE DEVICE
BUSY
The Modbus slave informs the gateway that it is already in the process of
running a command and therefore it cannot run the one transmitted to it.
So the gateway should re-transmit the query subsequently.
16#07
(1)
NEGATIVE
ACKNOWLEDGE
The Modbus slave informs the gateway that it cannot process the requested
command. This exception only affects commands 13 and 14 (16#0D and
16#0E). These functions are not part of the standard Modbus commands and are
not described in this document.
16#08
(1)
MEMORY PARITY
ERROR
The Modbus slave informs the gateway that it has detected a parity error on the
access to its own memory. This exception only affects standard commands 20
and 21 (16#14 and 16#15) which are not supported by the gateway.
(1) Please see the standard Modbus documentation for further information about these various scenarios.