Schneider Electric VW3 A3 303 user manual Read non-existent or protected parameters

8. Modbus protocol

8. 13. Read non-existent or protected parameters

If a set of parameters is read using a Modbus function, the value returned for non-existent and protected parameters is equal to 16#8000.

If the same Modbus function is used to read parameters, all of which are non-existent or protected, the drive sends back an exception response with an error code equal to 2.

Example of non-existent or protected parameters being read:

In this example, the same request to read a non-existent parameter followed by 2 existing parameters is used several times in a row in order to demonstrate the effects of parameter protection.

The "Read Holding Registers" request (3) is addressed to a drive with a Modbus address of 12 (16#0C). The read operation is performed for 3 consecutive words, starting with address 8400.

Logic address	Parameter	Value
8400 = 16#20FA	Non-existent	-
8401 = 16#20D1	[Profile] (CHCF)	3
8402 = 16#20D2	[Copy channel 1 ↔ 2] (COP)	2

Request:

Slave no.	Request code	No. of 1st word		No. of words			CRC16
		Hi	Lo	Hi	Lo	Lo		Hi
0C	03	20	D0	00	03	0E		EF

Response:

Scenario no. 1: Parameters CHCF (8401) and COP (8402) not protected V Successful reading of these two parameters and value equal to 16#8000 for the non-existent parameter located at address 8400.

Slave no.	Response code	No. of bytes read	Value 8400		Value 8401		Value 8402		CRC16
			Hi	Lo	Hi	Lo	Hi	Lo	Lo	Hi
0C	03	06	80	00	00	03	00	02	17	E4

Scenario no. 2: Parameter CHCF (8401) protected and COP (8402) not protected V Successful reading of COP and value equal to 16#8000 for the non-existent parameter located at address 8400 and for parameter CHCF.

Slave no.	Response code	No. of bytes read	Value 8400		Value 8401		Value 8402		CRC16
			Hi	Lo	Hi	Lo	Hi	Lo	Lo	Hi
0C	03	06	80	00	80	00	00	02	CE	24

Scenario no. 3: Parameters CHCF (8401) and COP (8402) protected V Exception response (response code = 16#80 + request code), as all the parameters read are either non-existent, or protected; error code equal to 2 (the word addresses indicated in the request do not exist in the slave).

Slave no.	Response code	Error code	CRC16
			Lo	Hi
0C	80+03 = 83	02	51	32

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