GE RX3i - Page 169

Chapter 9. Modbus/TCP Client
156 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q
Command 3004, Example 2 – Write Single Coil
Set 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 Block
Word 2 00000 (0000) Always 0 (no-wait mode request)
Word 3 00008 (0008) Memory type of CRS word (%R)
Word 4
13
00009 (0009) CRS word address minus 1 (%R10)
Word 5 00000 (0000) Reserved
Word 6 00000 (0000) Reserved
Word 7 03004 (0BBC) Write to a Modbus/TCP Device
Word 8 00006 (0006) Channel number (6)
Word 9 00005 (0005) Modbus Function Code – Write Single Coil
Word 10 00072 (0048) Local PLC Memory Type
Word 11 00004 (0004) Local PLC Starting Address
Word 12 00501 (01F5) Address in the Remote Device
Word 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 with
the 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 the
Ethernet interface will get the data to be written to the remote PLC. Valid values for Word 10 are listed on page
150.
(Word 11) Local PLC Starting Address: Word 11 determines the starting address in the local PLC from which
the data is to be written. The value entered is the offset (1-based) from the beginning of PLC memory for the
memory type and mode specified in Word 10. This offset will be either in bits, bytes, or words depending on the
mode 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 remote
device. 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 a
Modbus Slave on a multi-drop link. The Modbus/TCP Unit Identifier is a special control code used in a
Modbus/TCP message block.