44 Rockwell Automation Publication 1420-UM001E-EN-P - March 2016
Chapter 4 Communication
The PowerMonitor 500 unit supports the following Modbus functions:
• 0x03 - Read n Holding Registers
• 0x04 - Read n Input Register
• 0x06 - Write one Holding Register
• 0x10 - Write multiple registers
• 0x08 - Diagnostic (with subfunction code 0x00)
• 0x42 - Read n Special Registers (vendor specific)
• Broadcast mode (write command on address 00h)
In this section, Modbus addresses are indicated in two ways. The ‘Modbus
address’ is expressed as the 6-digit input register address (example: 300123), used
with Modbus function code 0x04. The ‘Physical address’ is the hexadecimal
representation of the word address that is included in the communication frame.
Modbus function 0x04 can be used with the Modbus address by substituting a 4
for the first digit (example: 400123). With that distinction, functions 0x03 and
0x04 return the same data.
To avoid errors due to signal reflections or line coupling, a termination resistor
must be connected at the RS-485 ports of the master station and of the furthest
power monitor from the master station. In the PowerMonitor 500, you can
implement a jumper between (B+) and (T) to apply the required termination
resistance between (A-) and (B+) internally. Termination on both ends is
necessary even in case of point-to-point connection, with short distances.
The GND connection is optional if a shielded cable is used. For connections
longer than 1000 m (3280 ft), a line amplifier is necessary.
Data Types Supported
The IEEE754 representation of a 32-bit Floating Point number as an Integer is
defined as follows.
Va l u e = (-1)
sign
*2
(Exponent-127)
*1.Mantissa
Format Description Bits Range
INT Integer 16 -32768…32767
UNIT Unsigned Integer 16 0… 65535
DINT Double integer 32 -2
31
… 2
31-1
UDINT Unsigned Double Integer 32 0…2
32-1
ULINT Unsigned long Integer 64 0…2
64-1
REAL Single-precision Floating Point 32 -(1+[1-2
-23
])x2
127
…2
128
Bits
31 30…23 22…0
Sign Exponent Mantissa
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