Deister Electronic GmbH UDL500 사용자 설명서
3. RS485 interface
Most RS485-buses require termination resistors across the conductor pair. The need for
termination has to be checked for each installation. Especially for high data rates, steep
edges or long cables termination resistors are absolutely mandatory. Only both ends of the
main cable, i.e. at the first and the last device, require termination resistors, additional
resistors excessively load the drivers. The resistor value matches the cable´s differential
mode characteristic impedance (in most cases 100 ... 120Ω).
termination has to be checked for each installation. Especially for high data rates, steep
edges or long cables termination resistors are absolutely mandatory. Only both ends of the
main cable, i.e. at the first and the last device, require termination resistors, additional
resistors excessively load the drivers. The resistor value matches the cable´s differential
mode characteristic impedance (in most cases 100 ... 120Ω).
Attention!
This termination resistor (Terminator, 120Ω) has been factory built-in into
all UDL500 and has to be removed if necessary (see chapter 2).
This termination resistor (Terminator, 120Ω) has been factory built-in into
all UDL500 and has to be removed if necessary (see chapter 2).
At the RS485-bus you need a controller with fail-safe biasing meaning a pull-up and a
pull-down resistor on the cable. The fail-safe biasing provides a known-state, in which
there is no active driver on the bus. Therefore this is absolutely mandatory regardless of
data rates and length of cables.
pull-down resistor on the cable. The fail-safe biasing provides a known-state, in which
there is no active driver on the bus. Therefore this is absolutely mandatory regardless of
data rates and length of cables.
Technical data (for baud rates up to 100kBps):
Max. bus length:
1200m (4000 feet)
Max. stub length:
because of reflections stubs should be kept as
short as possible; exceptions allow a length up
to 5m (16 feet)
short as possible; exceptions allow a length up
to 5m (16 feet)
Recommendation for the cable:
twisted pair, cable-cross section at least
0.22mm
0.22mm
2
(AWG 24) differential-mode
characteristic impedance 100 ... 120Ω
V17/01/08
deister electronic GmbH 30890 Barsinghausen Germany
9
Wiring & Installation Instructions UDL500