Exception Responses - Siemens 7XV5673 Device Manual

8 Communication
8.2 Modbus
8.2.2

Exception Responses

NOTE
The exception responses for Modbus TCP and Modbus UDP (Ethernet) and Modbus RTU (serial) are the
same.
The Modbus server performs a series of consistency checks of the Modbus client requests, and if errors (for
example request to read a nonexistent register) are detected, it generates Modbus exception codes which are
signaled to the Modbus client in exception responses messages.
The messages contain the following codes:
Exception-Code 01 ILLEGAL_FUNCTION
• The Modbus client uses a function that is not supported by the Modbus server of the SICAM I/O Unit (the
supported Modbus functions are listed in chapter 8.2.1).
Exception-Code 02 ILLEGAL_DATA_ADDRESS
• An attempt is made to read out or write to a nonexistent Modbus register (see chapter 8.2.8, Modbus
mapping for valid registers).
• An attempt is made to read out or write to too many registers. A Modbus message enables reading out
125 holding registers and writing to 123 holding registers maximum.
• The Modbus clients tries to write to a register in the Modbus server for which only read access is allowed
according to the Modbus mapping (see chapter 8.2.8).
Exception-Code 03 ILLEGAL_DATA_VALUE
• The Modbus client addresses a register, for which the access to partial data was not released.
• The Modbus client attempts to write to the Modbus server for which the access rights are set to "read only".
• The Modbus client, the I/O mirror server, or the I/O mirror client (Ethernet or serial) tries to control the
writing of the Indication from Remote indication into the register of the SICAM I/O Unit. If the SICAM I/
O Unit is configured as I/O mirror server or I/O mirror client (apart from I/O mirror server, serial, unidirec-
tional), the Indication from Remote indication is only controlled via the I/O mirror.
Exception-Code 04 SERVER_FAILURE
• Error during the time format conversion in the Modbus server because a faulty date/time format was
received via Modbus (for example month format > 12).
140 SICAM I/O Unit, 7XV5673, Device Manual
E50417-H1040-C484-A3, Edition 05.2012