Environmental Manager: Main Module 9
How to wire Modbus
The Modbus interface supports 2-wire RS-485, plus
ground. Modbus can be configured to communicate
at either 9600 or 19200 bps. The default setting is
9600 bps.
Modbus requires both termination and polarization
resistors at the bus master. Each end of the bus
requires a 150-ohm resistor, and the bus also requires
a 400–650-ohm resistor from D1 to +5 Vdc and from
D0 to GND.
For more information, see the Modbus
standard at www.modbus.org. Search
for the Modbus Serial Line
Implementation G uide.
Installation—Accessories
Sensors
Selecting a location for the sensor:
Install the sensor in a lo cation that represents the ai r
to be monitored. Avoid placing the sensor anywhere
that may affect the sensor reading, such as near
windows, room entrances, air ducts, other heat
sources, or in direct sunlight.
UNIT 2
499 OHM
+5V
499 OHM
GND D0 D1
UNIT 1
CONTROLLER
150 OHM
G
N
D
DD
0
1G
N
D
DD
01
SHIELD
TO
GND
TWISTED
PAIR
D0 & D1
SHIELD
TO
GND
TWISTE
D
PAIR
D0 & D1
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