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ManualsBrandsPhoenix Contact ManualsAutomationEnergy Meter, 35 ... 690 V, 4 kA, MODBUS/TCP/PROFINET RT/RJ45
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Communication
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The following questions regarding the behavior of a gateway remain open:
– Forwarding the broadcast in the RTU network.
Since there is no broadcast in the case of Modbus/TCP, it is not defined whether or not
the MBAP address 0 is forwarded in the RTU network by the Modbus gateway.
– Response messages with the unit identifier 0.
Neither is there a definition on whether the gateway itself generates an answer to mes-
sages with a unit identifier of 0.
By default upon delivery, devices of the EMpro product family behave as follows:
The EMpro does not forward messages with unit identifier 0 to the RTU network as broad-
cast. Furthermore, the EMpro itself responds to the query as Modbus TCP server.
Timing in gateway mode
As gateway, the EMpro acts as Modbus master on the Modbus/RTU side and forwards que-
ries to the addressed slaves.
As Modbus/RTU master, the device requires a time-out for queries. If this time-out has ex-
pired without a response from the Modbus/RTU slave, the gateway replies to the Mod-
bus/TCP client with an error message.
By default upon delivery, the duration for the time-out is 250 ms.
Unsuitable time-out settings both at the gateway and and at the querying Modbus/TCP cli-
ent can cause unwanted problems.
Problems can occur if the time-out times at the Modbus/TCP client or EMpro in gateway
mode are too short, or if the ratios between these two time-out times are unfavorable.
The time-out setting has to be individually configured based on the application.
Nevertheless, the following recommendations can be given; they should work in normal
cases.
– The default setting of the EMpro is adequate for most applications.
– If there are slaves with slow response times in the RTU network, the time-out setting of
the gateway should be increased.
– If very slow Baud rates are used on the RS-485, the time-out setting of the gateway
should be increased.
– The time-out duration of the querying Modbus/TCP client should always be longer than
that of the gateway.