OBID
®
Installation
ID RWA02.ABC
FEIG ELECTRONIC GmbH
Page 29 of 36
E N G L I S H
3.6 RS485 Interface (ID RWA02.ABC-B)
With RS485 data buses, it can be necessary to use terminating resistors. For each installation,
checks should be made as to whether it is necessary to use terminating resistors, because this
e.g. is dependent on line lengths, bus structure, powering of the Readers and the employed host
computer. Generally, a terminating resistor is only required at the end of the bus, i.e. on the last
unit. In order to do this, the Jumper needs to be pit on X2 terminals 1 and 2 (see Fig 8 and Fig 5).
To operate the bus, you need a host computer with a terminating resistor and active termination. A
twisted paired or stranded wire is recommended.
Host
without termination
R/A
T/B
ID RW02
(with active termination)
with termination resistor
A
B
X2
ID RW02
X2
ID RW02
X2
T/B
T/B
R/A
R/A
Fig 8: data bus with RS485 interface
If no host computer with active termination is available, an active termination can be implemented
as an alternative at maximum one Reader. The Jumpers X3 and X4 are available to this.
1 2 3
X2
X3
X4
1 2 3
X2
X3
X4
1 2 3
X2
X3
X4
without termination
(default)
with termination
resistor
active termination and
termination resistor
Fig 9: Jumper positions of the RS485 interface
Fig 10: intern construction of the RS485 interface
X2
X3
X4
+5V
GND
1
T / B
R / A
1
1
1 k
Ω
1 k
Ω
100
Ω
