Chapter 9. Modbus/TCP Client
GFK-2224Q January 2017 147
Close a Modbus/TCP Client Connection (3001)
The application program closes a Modbus/TCP Client Connection by issuing the Close Modbus/TCP Client
Connection COMMREQ. The Close COMMREQ closes the underlying TCP connection and frees the channel for
other communication tasks.
An error response is returned if the channel number in the COMMREQ identifies a non-Modbus/TCP Client
connection or an inactive channel.
Command 3001 Example
Terminate the Modbus/TCP Client connection established on Channel 5. Return the COMMREQ Status word to
%R10.
Dec (Hex)
Word 1 00002 (0002) Length of Channel command Data Block
Word 2 00000 (0000) Always 0 (no-wait mode request)
Word 3 00008 (0008) Memory type of CRS word (%R)
Word 4
13
00009 (0009) CRS word address minus 1 (%R10)
Word 5 00000 (0000) Reserved
Word 6 00000 (0000) Reserved
Word 7 03001 (0BB9) Close Modbus/TCP Client Connection
Word 8 00005 (0005) Channel number (5)
(Word 7) Channel Command Number: Word 7 requests the Close channel service.
(Word 8) Channel Command Number: Word 8 identifies a channel previously opened with an Open
Modbus/TCP Client Connection request. If a Close Modbus/TCP Client Connection is sent to a channel that is
already closed, a success CRS value of 1 will be returned.
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