EverFocus EDR-1640 - Manual (Page 20)

A direct RS-485 bus star wiring is not supported; star wiring requires the use of signal
distributors.
Improper RS-485 bus star wiring
If star wiring is inevitable, EDA 997A RS-485 signal distributors may be used. The maximum system
cable length can also be expanded by using these distributors, physically providing a new RS-485
bus with 1200 m cable length each at every distributor output.
Star wiring with RS-485 signal distributor
ATTENTION: The RS-485 signal distributor EDA997A is unidirectional! This means that the
signal only flows from the input towards the outputs. Therefore, e.g. the
interconnection of several keyboards is not possible with this signal distributor!
In case the maximum number of 32 bus participants is exceeded, the number of connected
devices can be increased by using RS-485 distributors. Each distributor output physically
provides one RS-485 bus which enables the additional connection of 31 further devices (the
distributor output represents one bus participant itself).
The maximum system expandability depends on the RS-485 address range of the installed
devices.
System expansion with RS-485 signal distributor
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