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GFK-1541B Chapter 4 Programming Modbus/TCP Channel Commands 4-9
4
Command 3000 Example
Establish a channel (Channel 5) to a remote Modbus/TCP device at IP address 10.0.0.1. Return
the COMMREQ Status word to %R10.
Dec (Hex)
Word 1
00008 (0008) 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 03000 (0BB8) Open Modbus/TCP Client Connection
Word 8 00005 (0005) Channel number (5)
Word 9 00001 (0001) Remote Device Address Type
Word 10 00004 (0004) Length of Remote Device Address
Word 11 00010 (0010) Numeric value of 1
st
Octet
Word 12 00000 (0000) Numeric value of 2
nd
Octet
Word 13 00000 (0000) Numeric value of 3
rd
Octet
Word 14 00001 (0001) Numeric value of 4
th
Octet
* 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 is the command id for an Open Modbus/TCP
Client Connection COMMREQ. If successful a TCP connection with the specified device is
allocated.
(Word 8) Channel Number:
Word 8 specifies the channel number to allocate for the Modbus/TCP
Client connection. Channels 1-16 can be used for Client communications.
(Word 9) Address Type:
Word 9 specifies the type of IP Address specified for the remote device.
A value of one (1) is required in this word.
(Word 10) Length of IP Address:
Word 10 specifies the length of the IP Address. A value of
four (4) is required in this word.
(Word 11) IP Address 1
st
Octet:
Word 10 specifies the value of the first octet of the IP Address.
(Word 12) IP Address 2
nd
Octet:
Word 11 specifies the value of the second octet of the IP
Address.
(Word 13) IP Address 3rd Octet:
Word 12 specifies the value of the third octet of the IP
Address.
(Word 14) IP Address 4th Octet:
Word 13 specifies the value of the fourth octet of the IP
Address.