Schneider Electric VW3A3310d user manual List of Modbus functions supported, Byte Meaning

11. Modbus TCP server

11. 4. List of Modbus functions supported

	Code	Modbus name	Description	Size of data
	(decimal)
3 = 16#03		Read Holding Registers	Read N output words	63 words max.
6 = 16#06		Write Single Register	Write one output word	-
16	= 16#10	Write Multiple Registers	Write N output words	61 words max.
23	= 16#17	Read/Write Multiple Registers	Read/write N words	20/20 words max.
43	= 16#2B	Read Device Identification	Identification	-

11. 5. “Read Holding Registers” (3) function

This Modbus request is used to read the values of a number (No. of Points) of adjacent words starting at the address indicated (Starting Address). The values read are restored one after another, at the end of the response (First Point Data →Last Point Data).

Request format:

Byte Meaning

0Function Code = 16#03

1Starting Address Hi

2Starting Address Lo

3No. of Points Hi (0)

4No. of Points Lo (1 - 125)

Response format:
Byte	Meaning
0	Function Code = 16#03
1	Byte Count (B = 2 × No. of Points)
2	First Point Data Hi
3	First Point Data Lo
…	………………………
B	Last Point Data Hi
B+1	Last Point Data Lo
Exception response format:
Byte	Meaning	With the VW3A3310d Ethernet card
0	Function Code = 16#83
		01 (Illegal Function)
1	Exception Code	02 (Illegal Data Address)
		03 (Illegal Data Value)
		04 (Illegal Response Length)

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