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Modbus Transmission Control Protocol Configuration
Modbus TCP interface runs on an Ethernet connection. TCP makes sure all data is
received. Modbus TCP is a non-streaming data interface standard. This means data must
be requested in order for it to be received. The Modbus TCP Interface will store all data
values in 16-bit registers. The registers and their associated data fields are mapped below.
To access the sensor holding registers for a particular device, the assigned slot number for
the device needs to be known. When reviewing added devices through the default server,
the order in which devices are presented may not necessarily correspond to the order
in which the devices are stored in the gateway network list as the default server will sort
the devices based on their ID. To be certain which device is in a particular slot, go to the
gateway local web interface wsn.htm page or status page and note which slot the desired
device is assigned to.
After the slot number(s) for the desired devices to read from are known, the following
formula may be applied to determine the correct starting register to read from to retrieve
the recorded data from the device: starting register=101+16(slot no.-1). Each reading will
report the most recent message received from that device by the gateway, so the polling
frequency should be greater than the device heartbeat frequency to avoid missing device
updates.
