7SJ61/62/63 6MD63 - Modbus
C53000-L1840-C001-01
3-1
3 Exception responses of the Modbus slave
Exception responses of the
Modbus slave
3
If the Modbus slave receives a query from the Modbus master which
cannot be processed (e.g. a request to read a non-existent register),
then the slave answers with an exception response message.
The following exception codes are signaled in a exception response
message to the Modbus master by the Modbus slave of the SIPROTEC
device:
Exception code 01
ILLEGAL_FUNCTION
The function code used in the query by the Modbus master is not
supported by the Modbus slave of the SIPROTEC device.
Ref to chap. 2 for a list of supported Modbus functions.
Exception code 02
ILLEGAL_DATA_ADDRESS
The Modbus master addresses in the query a register for which:
• no mapping entry exist (i.e. a non-existent register),
• the access is not enabled since the addressed register is part of a
complex bus object which uses more than one registers and can be
read only completely.
Exception code 03
ILLEGAL_DATA_VALUE
The Modbus master tried to write to a register for which only read
access is permitted.
Exception code 06
SLAVE_DEVICE_BUSY
The Modbus slave has no valid mapping data or the Modbus registers
still have not been initialized and enabled by the SIPROTEC device
(after initial start or restart of the device).
Exception code 08
NEGATIVE_ACKNOWLEDGE
If at the diagnostic query (Modbus function code 8) another subfunction
than 00 or 02 is requested, then this is rejected with
NEGATIVE_ACKNOWLEDGE.
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