Honeywell WEB-VA00IB24NM Installation Instructions Manual page 21

— Must conform to TIA/EIA 485 cabling guidelines.
"TIA/EIA 485 Cable Specifications" on page
See
14.
— Should not extend beyond a single building.
— It is recommended that you select a low baud rate (for
example, 19.2 kbps) for reliable operation.
120Ÿ
16 17
18
GND
+5V
ISO
GND
550 OHM
550 OHM
GENERIC
RS485 (-)
Modbus
RS485 (+)
DEVICE #2
RSxN
(SLAVE)
Modbus Device #1
(MASTER)
2 3
F1
24 V
230 V
Figure 3. Modbus Master Controller and Connected Modbus
Slaves (with inserted termination resistors)
L
TWISTED
PAIR
NOTE 1
120Ù
GENERIC GENERIC
Modbus Modbus
DEVICE #N-1 DEVICE #N
(SLAVE) (SLAVE)
21
Prelim Draft - Brand Neutral
BACNET IP/MSTP VAV - INSTALLATION INSTRUCTION
With regards to Figure. 3 above, note the following:
NOTE:
NOTE:
1. If any of the devices are electrically isolated, it is
recommended that those devices be connected to the
ground terminal (GND), if available.
"TIA/EIA 485 Cable Specifications" on page
See
14.
2. The 120-Ohm termination resistor must be inserted
directly into the terminals of both end devices.
3. If shielding is used, the shielding of each individ- ual bus
segment should be separately connected at one end to
earth.
4. Always power each controller and the connected slaves
via separate transformers.
5. Between devices equipped with non-isolated RS485 bus
interfaces, potential differences of max. ±7 V are allowed.
Further, this bus should not extend beyond a single
building.
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