10. easyE4 communication Connection to other devices
10.17 Modbus TCP
Unit ID
Some Modbus TCP servers evaluate the unit ID in order to forward to submodules
(e.g., Modbus RTU modules). One example of this is when multiple Modbus TCP serv-
ers are working through a Modbus TCP bridge with the same IP address.
In this case, Modbus TCP server read and write access is only possible with the unit
ID. For Modbus TCP, the default setting is 255.
Accordingly, please check whether the Modbus TCP server being used is evaluating
the unit ID and, if necessary, set the required unit ID.
Update Rate
The update rate defines the time intervals at which requests will be sent
to the Modbus TCP server. The value range is 30 to 10,000 [ms], with the default
value being 100 [ms]. Moreover, the value can be changed in increments of 10 [ms].
The update rate should not be too low so as to ensure that the Modbus TCP server's
communication load will not become excessive. Please note that the actual real-life
time intervals may deviate from the setting depending on the easyE4 base device's
load.
Function Code
easyE4 supports the following function codes as a Modbus TCP client:
FC
dec
Function description Function code
hex
FC1
Read Coils  0x01
FC2
Read Discrete Inputs  0x02
FC3
Read Multiple Holding Registers  0x03
FC4
Read Input Registers  0x04
FC5
Write Single Coil  0x05
FC6
Write Single Holding Register  0x06
FC15
Write Multiple Coils  0x15
FC16
Write Multiple Holding Registers  0x10
FC23
Read and Write Multiple Holding Registers  0x17
Start addr.
The address of the first Modbus TCP server element that should be written to or read.
The value range is 0 to 65535.
Keep the 0-based address system in mind.
If the address range does not match the Modbus server's address range
because the former starts from 0 and the latter from 1, you will need to
use an offset.
In this case, you will need to set the start address to the original value
minus 1.
Alternatively, the option Auto-decrement on all addresses can be
activated with a checkmark.
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easyE402/24 MN050009ENEaton.com
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