Rs485 Interface - Honeywell EK205-M Operating Instructions Manual

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8.2.2 RS485 interface

8.2.2.1 Connection
i
These applications only work with an external power supply to the EK205-M, not in
battery mode
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If an EK205-M is connected to an RS485 bus, no terminal resistors may be connected to
the bus!
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Connect the RS-485 interface in safe assembly area only. Modem power needs to be
unplugged and removed from the enclosure to access the RS-485 interface in the field.
As a result of its current limit to obtain approval as an intrinsically safe apparatus, the EK205-
M cannot supply enough current for the terminal resistors. The terminal resistors are not
required for the data transfer rates used.
If terminal resistors are essential in your application, connect the devices as described in section 8.2.2.1.2.
i
For EMC reasons, we recommend that the subscribers are galvanically isolated from
each other at the bus. You should therefore give preference to the installation described
in section 8.2.2.1.2.
8.2.2.1.1 Two-wire simplex wiring (RS485 mode)
.
Data transfer