Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 User Manual, Firmware rev. 3.0 or LATER - Manual (Page 93)

Publication 1404-UM001F-EN-P - November 2009 93
Communication Chapter 4
The power monitor does not initiate Modbus commands but responds
to commands sent by the Modbus master. The following Modbus
function codes are supported:
•
03 Read Holding Registers
•
04 Read Input Registers
•
16 Write Multiple Holding Registers
•
08 Diagnostics
– 00 Echo Command Data
– 02 Return Diagnostic Counters
– 10 Clear Diagnostic Counters
•
06 Write Single Holding Register
Function 06, 16 and the sub function 10 of function 08 support
Broadcast packets.
Refer to Appendix A for Modbus addresses of the power monitor data
tables.
The power monitor supports zero-based addressing. The address
ranges are arranged as follows (note that not all addresses in the
range are used):
•
30,001…40,000 Modbus Input Register (Analog Input) Address
Space
•
40,001…50,000 Modbus Holding Register (Analog Output)
Address Space
The Modbus protocol supports four types of data: Discrete Input, Coil,
Input Register and Holding Register. The power monitor supports
Input Registers (read-only) and Holding Registers (read-write or write
only).
Input Registers and Holding Registers are 16 bits long. Floating point
values in the data tables are represented as big-Endian two-register
arrays in IEEE-754 floating point format. The Modbus client
application must be able to reassemble the two-word array into a
valid floating-point value.
The power monitor returns the Modbus error codes shown in the
table below when appropriate. In the event of an exception reply, not
only is the exception code sent to the master device, but also the
power monitor slave’s diagnostic counter records the error code to
further explain the error reason.