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PROTOCOL COMMANDS
The Modbus messaging protocol used for communication follows the Modbus RTU protocol described in
this section. Each register read from or written to the PowerScout is a 16-bit unsigned, positive integer
value. The PowerScout supports the following commands.
Command Name
Command
Number (Hex)
Description
Read Holding Registers 03 Used to read the data values from the PowerScout.
Write Single Register 06 Used to write a single holding register to a PowerScout.
Report Slave ID 11 Used to read information from the identified PowerScout.
Table IV-1: Supported Modbus Commands
The following guidelines are used for these Modbus commands:
All values are hexadecimal, spaces are not included.
The address is the value of the address switch on the PowerScout. This must be different fo
r
e
ach PowerScout on a single Modbus network.
The register’s high-order and low-order bits are the 16-bit value of a single, or first, register to
be accessed for a read or write.
The CRC is the 16-bit CRC value. Note that the CRC's LSB and MSB are reversed in comparison to
those for the registers and data.
Read Holding Registers
This command reads the contents of a contiguous block of holding registers containing data values from
the PowerScout. When a read command is received, the PowerScout sends a response that includes the
values of the requested registers.
Command Information
Command
Layout
Example
Command
PowerScout address nn 37
Command number 03 03
First register to read – high order bits xx 00
First register to read – low order bits xx 0C
Number of registers to read – high order bits xx 00
Number of registers to read – low order bits xx 01
CRC low order bits xx 41
CRC high order bits xx 9F
Table IV-2: Format for Modbus Command 03
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