Rockwell Automation 1425 PowerMonitor Wireless 250 - Manual (Page 48)

48 Rockwell Automation Publication 1425-UM001A-EN-P - January 2012
Chapter 3 Software Interface
The ongoing recording intervals in the PowerMonitor W250 units will be
disrupted by a change of the PC Receiver time.
Modbus Command Interface
The Wireless Mesh Network communicates with client devices by using the
Modbus RTU protocol. Modbus ASCII is not supported. Please refer to the
Modbus Application Protocol Specification, v1.1b, December 28, 2006, available
from
http://www.modbus.org .
A client application acting as a Modbus RTU Master communicates through the
PC Receiver to obtain data (and issue commands) to end devices (power
monitors) in the wireless network. The PC Receiver may be directly addressed by
using Modbus address 247.
In this mode, the following commands are supported:
• Read Holding Registers (0x03)
• Write Multiple Registers (0x10)
• Read Device Identification (0x2B/0x0E)
The PC Receiver also acts as a proxy for the power monitors in the network. As
described earlier, the power monitors periodically broadcast data to the PC
Receiver. The PC Receiver in turn buffers the data and responds to commands
issued by the Modbus Master that are addressed to the power monitors. Available
Modbus commands are:
• Read Holding Registers (0x03)
• Write Multiple Registers (0x10)
The PC Receiver will respond to a write command with an ‘acknowledge’
exception code 0x05. This indicates the server (or slave) has accepted the request
and is processing it, but a long duration of time will be required to do so. This
response is returned to prevent a time-out error from occurring in the client (or
master). The client (or master) can next issue a Poll Program Complete message
to determine if processing is completed. (From the Modbus Application Protocol
Specification, v. 1.1b, December 28, 2006.)
IMPORTANT When setting the time in the PC Receiver, both UTC registers need to be written
in one command.
IMPORTANT ASCII mode is not supported.
IMPORTANT Response of a write command will always be an ‘acknowledge’ response.To
verify if a write command is successful, poll the register that it was written to.