60
P
ROTOCOL
C
OMMANDS
The Modbus messaging protocol used for communication follows the Modbus RTU protocol described in
this section. Each register read from or written to the Power Patrol is a 16-bit unsigned, positive integer
value. The Power Patrol supports the following commands.
Command Name
Command
Number (Hex)
Description
Read Holding Registers
03
Used to read the data values from the Power Patrol.
Write Single Register
06
Used to write a single holding register to a Power Patrol.
Report Slave ID
11
Used to read information from the Power Patrol.
Table D-3: Supported Modbus Commands
The following guidelines are used for these Modbus commands:
All values are hexadecimal/decimal, depending on your meter, spaces are not included.
The address is the value of the address switch on the Power Patrol. This must be different for
each Power Patrol 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 Power Patrol. When a read command is received, the Power Patrol sends a response that includes
the values of the requested registers.
Command Information
Command
Layout
Example
Command
Power Patrol 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 D-4: Format for Modbus Command 03
