Communication-capable Circuit Breakers

WL Circuit Breaker

Function 03: Read Holding Registers

Function

This function reads a set of registers from a COM16 slave.

 

 

 

 

Start Address

Any value within the address range defined for each of the data sets. If any other address is specified,

 

an Exception Code of 02 (Invalid Data Address) will be returned.

 

 

 

Quantity of Registers

If “Quantity of Registers” is not in the range of 1 to 125, an Exception Code of 03 (Invalid Data Value)

 

will be returned. If the “Quantity of Registers” is not correct for the Dataset indicated by the “Start

 

Address”, an Exception Code of 02 (Invalid Data Address) will be returned.

 

 

 

Example:

Request Message to slave

The following is an example of a request to read Dataset 0 from a COM16 slave device at

MODBUS address 7. The length of Dataset 0 is 4 bytes.

07H

Slave Address

03H

Function Code

00H

Register Start Address "High" (Dataset 0 address is 0000 hex)

b7H

Register Start Address "Low"

00H

Quantity of Registers "High" (Register quantity is 4 decimal)

04H

Quantity of Registers "Low"

xxH

CRC Check Code "Low"

xxH

CRC Check Code "High"

Reply Message from slave

The response returns 2 registers containing the contents of Dataset 0.

07H

Slave Address

 

03H

Function Code

 

04H

Byte Count (Bytes returned is 4)

00H

Register Address 00H Data "High"

03H

Register Address 00H Data "Low"

00H

Register Address 00H

Data "High"

00H

Register Address 01H

Data "Low"

xxH

CRC Check Code "Low"

xxH

CRC Check Code "High"

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WL MODBUS Communication and Electronic Accessories • January 2005

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Siemens UL1066, UL 489 specifications Function 03 Read Holding Registers, Request Message to slave, Reply Message from slave

UL 489, UL1066 specifications

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