Device communication
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isoxx1685Dx-x25_D00272_07_M_XXEN/09.2022
9. Device communication
Over the RS-485 interface of the device, data can be transferred either via the BMS protocol or
the Modbus RTU protocol. The protocol and the protocol parameters are set in the "Interface"
menu 8.2 (6.3).
9.1 RS-485 interface with BMS protocol
The RS-485 interface, galvanically isolated from the device electronics, serves as a physical
transmission medium for the BMS protocol. When an ISOMETER® or other bus-capable devices
are interconnected via the BMS bus in a network, the BMS bus must be terminated at both
ends with a 120 resistor. For this purpose, the device is equipped with the terminating
switch RS-485 Term. (ON/OFF).
An RS-485 network that is not terminated is likely to become unstable and cause malfunctions.
Only the first and last device in one line may be terminated. Hence, stub feeders in the network
must not be terminated. The length of the stub feeders is restricted to a maximum of 1 m.
9.1.1 Topology RS-485 network
Connection to the terminals A and B.
Communication with EDS devices
Communication with EDS devices is only possible with the BMS protocol.
maximum length of the RS-485 network: 1200 m
1. device … device last device
stub feeder
max. 1 m
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