
EM-RS485 Modbus Protocol Guide
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154-0023-0B
To begin automatic configuration, simply connect the RS485 terminals to an active Modbus network. An
active Modbus network consists of a Modbus master device that regularly polls at least one Modbus slave
(whether the slave replies or not).
IMPORANT:
If a Modbus network has devices communicating with multiple baud rates and/or formats,
the automatic configuration result is unpredictable. Set the configuration manually with the
Setup Button
interface (see
Installation Instructions
) before connecting the meter in such an environment.
Once connected, the meter observes RS485 activity to learn baud rate, serial format, and protocol. Without
activity, the meter cannot learn! The meter will not interfere with existing network traffic during the
observation phase. As configuration proceeds, the
RS485 Status
LED indicates progress with a combination
of color and blinking activity patterns. Diagnostic mode conditions can help identify the current auto
configuration step (see Figure 2, and also the
Installation Instructions
).
Waiting For
Activity
Detecting
Baud Rate
Detecting
Protocol
Ready
Figure 2: Automatic Configuration Conditions
The
RS485 Status
LED turns green after at least one full frame successfully passes a CRC* integrity test.
Assuming no conflicts, the master can then use Modbus functions to query or configure registers.
The meter stores any discovered automatic configuration result in non-volatile memory and reloads them
whenever the meter resets (e.g. after power loss). The automatic configuration can be cleared by holding
down the
Setup Button
while resetting the meter (e.g. removing and reapplying power). User-configured
parameters will not be affected, but the meter must redetect any missing parameters before reestablishing
communication.
For permanent installations, the protocol configuration parameters (see
) may be set to lock the
baud rate, format, and protocol. However, this will prevent the meter from adapting to future changes in
the network environment.
The EM-RS485 supports the following Modbus device functions:
•
Diagnostics
•
Report Server ID
*
Cyclical Redundancy Check