5
8903/RS RS485 Communications Interface
Wiring the RS485 System
Technical Specification of the 8903/RS Option
Option Connector
Terminal X48
Pin Connection
1 B
2 Ground
3 A
4 T
(Terminator)
5 Screen
Figure 6. Terminal X48
Cable Specification
The
preferred cable
is a screened cable that has one twisted pair and a power core, or cable that
has at least two twisted pairs. Cat 5e STP screened (braid or braid+foil) cable is recommended.
An
alternative cable
is a screened cable that has one twisted pair. This should only be used on
short cable runs. See section
Maximum Cable Lengths
below.
RS485 bus:
Isolated 2-wire + ground
Receiver input resistance:
12 k
Ω
(one Unit Load)
Differential input threshold:
±200 mV
Differential driver output voltage:
±5 V max.
Fixed biasing:
10 k
Ω
pull-down resistor to terminal A
10 k
Ω
pull-up resistor to terminal B
Optional selectable termination:
120
Ω
in series with 10nF capacitor terminator
Number of nodes on one RS485 bus:
24 maximum including the master
1
2
3
4
5
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Содержание 8903/RS
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