GE GFK-1541B manual Command 3004, Example 1 Set Single Register

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Command 3004, Example 1 – Set Single Register

Write one register from %AI10 to address 40200 in the remote Modbus/TCP server. 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	00006	(0006)	Modbus Function Code – Preset Single Register
Word 10	00010	(000A)	Local PLC Memory Type
Word 11	00010	(000A)	Local PLC Starting Address
Word 12	00200	(00C8)	Address in the Remote Device
Word 13	00001	(0001)	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 Write Data to remote 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 6, Preset Single Register.

(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 register in the remote device.

(Word 13) Number Registers in Remote Device: Word 13 specifies the quantity of registers to write to the remote device. For Modbus Function Code 6, Preset Single Register 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.

GFK-1541B Chapter 4 Programming Modbus/TCP Channel Commands 4-17