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Section 3
Vendor-specific implementation
3.1.2.1
12
Modbus TCP usually shares the Ethernet connection with the other
Ethernet based protocols of the IED. The number of Ethernet based clients
that can be simultaneously connected to the IED is restricted.
TCP/IP interface configuration
The Modbus TCP/IP protocol uses the Ethernet interface. The general setup parameters of
Ethernet, for example the IED's own IP address, are found via the LHMI path
Configuration > Communication > Ethernet.
Client connections
The Modbus TCP/IP server accepts as many simultaneous client connections as defined
with the Max TCP/IP clients parameter:
• The setting range for the parameter is 0...5.
• If the parameter value is zero, the Modbus TCP/IP server connection is not in use.
• The parameter works in conjunction with the parameters of a registered Modbus
TCP/IP client.
When client X reconnects, the old connection of that client is disconnected and the new
connection is accepted to avoid zombie clients. When the maximum number of clients are
connected, a new connection request is handled as follows:
• If there are unregistered clients connected, the one with the longest silent period is
disconnected and a new connection is accepted.
• If there are only registered clients connected, the new connection request is rejected.
It is possible to predefine the client or clients which are always granted Modbus TCP/IP
connections by registering the clients' IP addresses. For example, if four concurrent
connections are allowed and three of them are registered, they are seen as Client
connection 1...Client connection 3. These three registered connections are then dedicated
to certain clients only and the fourth connection is available to other clients.
Client IP addresses
There are five Modbus setting parameters for Modbus client IP addresses. The parameter
value "0.0.0.0" indicates that the client IP address is not defined.
If there are, for example, four available TCP/IP connections defined and one of the
connections is to be dedicated for a certain client X, enter the client X's IP address to the
Client IP1 parameter. The IP addresses of the Modbus clients 2...4 can be set to "0.0.0.0".
The setting of the Modbus client5 IP address has no meaning in this example as the
connection is not in use. In this example, the TCP/IP session 1 is dedicated to the client X
which means that this registered client X is always able to connect to the IED.
Unregistered clients can connect to sessions 2...4. However, an unregistered client
connection request can be rejected if sessions 2...4 are already occupied. The write
authority can also be assigned differently for registered TCP/IP clients.
1MAC052634-MB D
615/620 series ANSI
Communication Protocol Manual
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