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4-12 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual
–
May 2002 GFK-1541B
4
Command 3003 Example 1
Read four Input Registers from Address 30200 in the remote Modbus/TCP device. Store the
registers at location %R20. 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 03003 (0BBB) Read from a Modbus/TCP Device
Word 8 00006 (0006) Channel number (6)
Word 9 00004 (0004) Modbus Function Code
Word 10 00008 (0008) Local PLC Memory Type
Word 11 00020 (0014) Local PLC Starting Address
Word 12 00200 (00C8) Address in the Remote Server
Word 13 00004 (0004) Number of Registers in the Remote Device
Word 14 00001 (0001) Unit Identifier
* 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 identifies the COMMREQ as a Read Data from
Modbus/TCP Device command block.
(Word 8) Channel Number:
Word 8 identifies the channel number previously allocated for
communication with the remote Modbus/TCP server.
(Word 9) Modbus Function Code:
Word 9 specifies Modbus Function Code 4, Read Input
Registers.