Chapter 9. Modbus/TCP ClientGFK-2224Q January 2017 149zero value to identify the failure. See the section “Status Data” later in this chapter for detailed CRS failurecodes.Command 3003, Example 1Read four Input Registers from Input Registers 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 BlockWord 2 00000 (0000) Always 0 (no-wait mode request)Word 3 00008 (0008) Memory type of CRS word (%R)Word 413 00009 (0009) CRS word address minus 1 (%R10)Word 5 00000 (0000) ReservedWord 6 00000 (0000) ReservedWord 7 03003 (0BBB) Read from a Modbus/TCP DeviceWord 8 00006 (0006) Channel number (6)Word 9 00004 (0004) Modbus Function Code (Read Input Registers)Word 10 00008 (0008) Local PLC Memory TypeWord 11 00020 (0014) Local PLC Starting AddressWord 12 00200 (00C8) Address in the Remote ServerWord 13 00004 (0004) Number of Registers in the Remote DeviceWord 14 00001 (0001) Unit Identifier(Word 7) Channel Command Number: Word 7 identifies the COMMREQ as a Read Data from Modbus/TCPDevice command block.(Word 8) Channel Number: Word 8 identifies the channel number previously allocated for communication withthe remote Modbus/TCP server.(Word 9) Modbus Function Code: Word 9 specifies Modbus Function Code 4, Read Input Registers.
