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Connection Example
148
890USE17700 April 2004
List of Supported
Function Codes
and Their
Descriptions
The following table lists the function codes that can be used by Modbus over TCP/
IP masters that communicate with the STB NIP 2212:
Modbus over
TCP/IP Data
Exchange
The following table describes the general process used by Modbus over TCP/IP
masters to exchange data with the STB NIP 2212.
List of Exception
Codes
The following table describes the exception codes that Modbus over TCP/IP uses to
indicate an error condition:
Modbus
Function
Code
Subfunction
or Subindex
Hexadecimal Description
3 0x03 read output holding registers (4x)
4 0x04 read input registers (3x)
6 0x06 write single register (4x)
8 sub index 21 0x08 get/clear Ethernet statistics (See Ethernet
Statistics, p. 136)
16 0x10 write multiple (output) registers (4x)
22 0x16 mask write registers (4x)
23 0x17 read/write multiple registers (4x)
Stage Action
1 Execute a function, specify the function code and the register address of the
selected input or output channel.
2 The Modbus master (i.e., PC, PLC) sends a request to the STB NIP 2212.
If no exception is returned, the STB NIP 2212 responds to the master by
sending the data that was requested.
If a request contains an error, the STB NIP 2212 returns an exception code
to the master.
Code in Hexadecimal Description
0x01 illegal function
0x02 illegal data address
0x03 illegal data value
0x04 slave device failure