GE GFK-1541B manual Command 3004, Example 2 Force Single Coil

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Command 3004, Example 2 – Force Single Coil

Set coil 10501 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	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 – Force 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 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 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 Force 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 4-14.

(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, Force Single Coil this must be set to 1.

(Word 14) Unit Identifier: Default is 1. This field is typically used by Ethernet to Serial bridges to specify the address of a Modbus Slave on a multidrop link. The Modbus/TCP Unit Identifier is a special control code used in a Modbus/TCP message block. This value is 1 for most Modbus/TCP messages.

4-18 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual– May 2002 GFK-1541B