Rs-485 Serial Interface: Com3 - Arcom Director DS2 Hardware Manual

DS2/DS4 Hardware Manual
4.3.4

RS-485 Serial Interface: COM3

The last serial port on the DS2/DS4 (COM3) may be optionally configured for either RS-232 or RS-485
communication. SCT-AIM104 links JP1-JP4 must be in the "RS485" position to operate in this mode.
The RS-485 communication port is optically isolated. When COM3 on the Director is configured for two-
wire RS-485 operation, up to 32 devices can be connected together in a multidrop fashion. The following pin
configuration is used:
RS-485 is a balanced differential system, in which the voltage produced by the driver appears across a pair of
signal lines that transmit only one signal. A balanced line driver produces a voltage from 2 to 6 volts across
its positive and negative output terminals. A balanced differential line receiver senses the voltage state of the
transmission line across the two signal input lines.
is connected to the Data + of other 2-wire RS-485 devices.
Data +
is connected to the Data - of other 2-wire RS-485 devices.
Data -
should be connected to signal ground at one end of the cable network for grounding
GND
cable shield, not used by a balanced line receiver in determining the logic state of the
data line.
4.3.5 RS-485 / RS-422 Wiring Diagrams
When connecting RS-485 or RS-422 devices in a multidrop configuration, there must usually be a 120Ω
termination resistor on the first and last devices in the network, but not on any devices in the middle of the
loop.
In RS-485 or RS-422 systems, the ground connection is optional. It is typically used to connect the cable
shield for a shielded, twisted pair cable. In the DS2/DS4 COM3 port, the RS-485/422 ground is common with
the RS-232 grounds, but is isolated from the metal case. In order to avoid ground loops, connect the cable
shield to the RS-485/422 GND at only one point in the network.
DS-2, DS-3, DS-4 COM3 port
DB-9M (jumpers must be set
internally for RS-485)
1 RS-485 TX +
1
6 RS-485 TX -
5 GND
For DS-2/4, JP1 on SCT-AIM104 must
be set to the "RS-485" position.
For DS-3, LK2 on SCT-ORBCOMM
must be set to A, and LK3 must be B.
Drg. S15037-01d
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