Chapter 9. Modbus/TCP Client156 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224QCommand 3004, Example 2 – Write Single CoilSet coil 501 ON in the remote Modbus/TCP device using the value at %Q4. Return the COMMREQ Status word to%R10. Use channel 6, a channel previously opened with the Open Modbus/TCP Client Connection COMMREQ.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 03004 (0BBC) Write to a Modbus/TCP DeviceWord 8 00006 (0006) Channel number (6)Word 9 00005 (0005) Modbus Function Code – Write Single CoilWord 10 00072 (0048) Local PLC Memory TypeWord 11 00004 (0004) Local PLC Starting AddressWord 12 00501 (01F5) Address in the Remote DeviceWord 13 00001 (0001) Number of Coils in the Remote Device.Word 14 00001 (0001) Unit Identifier(Word 7) Channel Command Number: Word 7 identifies the COMMREQ as a Write Data to Modbus/TCP device.(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 5 Write Single Coil.(Word 10) Local PLC Memory Type: Words 10–11 specify the location in the local PLC from where theEthernet interface will get the data to be written to the remote PLC. Valid values for Word 10 are listed on page150.(Word 11) Local PLC Starting Address: Word 11 determines the starting address in the local PLC from whichthe data is to be written. The value entered is the offset (1-based) from the beginning of PLC memory for thememory type and mode specified in Word 10. This offset will be either in bits, bytes, or words depending on themode specified. Valid ranges of values depend on the PLC’s memory ranges.(Word 12) Remote Device Address: Word 12 specifies the destination coil address in the Modbus/TCP device.(Word 13). Number Coils in Remote Device: Words 13 specifies the quantity of coils to write to the remotedevice. For Modbus Function Code 5, Write Single Coil, this must be set to 1.(Word 14) Unit Identifier: This field is typically used by Ethernet to Serial bridges to specify the address of aModbus Slave on a multi-drop link. The Modbus/TCP Unit Identifier is a special control code used in aModbus/TCP message block.
