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4-10 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual
–
May 2002 GFK-1541B
4
Close a Modbus/TCP Client Connection (3001)
The application programcloses 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 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 4 (CRS word address) is the only zero-based address in the Command Block. Only this
value requires subtracting 1 from the intended address.
(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 a
Open Modbus/TCP Client Connection request. An unallocated channel results in an error
response.