Honeywell CENTRA LINE EAGLEHAWK Installation & Commissioning Instructions page 7

RS485 Interfaces
General
The EAGLEHAWK controller features two RS485 interfaces:

RS485-1 (consisting of push-in terminals 24 [GND-1], 25,
and 26) is isolated and can be used for any RS485-based
communication protocol available within Niagara
Ecosystems, e.g.: Panel Bus, BACnet MS/TP, etc.

RS485-2 (consisting of push-in terminals 29, 30, and 31
[GND-2]) is non-isolated (i.e. GND-2 is internally con-
nected with terminal 1 [24V~0]) and can be used for any
RS485-based communication protocol available within
Niagara Ecosystems, e.g.: Panel Bus, BACnet MS/TP,
etc.
RS485-1 Bias and Termination Resistors
RS485-1 is equipped with a three-position slide switch which
can be used to switch its bias resistors OFF (position "MID" –
this is the default), ON (position "BIAS"), and ON with an
additional 150Ω termination resistor (position "END").
3-POSITION SLIDE SWITCH
Fig. 10. RS485-1 three-position slide switch
The recommended slide switch setting depends upon the
location and usage of the given EAGLEHAWK – see Fig. 11
through Fig. 13 and Table 5; it also depends upon the
selected communication protocol (BACnet MS/TP, Panel Bus,
or Modbus RTU Master communication, respectively).
Table 5. Recommended slide switch settings
setting
Controllers located on either end of bus should have
END
this setting.
In small bus networks, a min. of one and a max. of
BIAS
two controllers should have this setting.
All other controllers (not set to "END" or "BIAS") on
MID
bus should have this setting (which is the default).
EAGLEHAWK CONTROLLER – INSTALLATION & COMMISSIONING INSTRUCTIONS
RS485-1
remarks
MID (DEFAULT)
RS485-1 (+)
RS485-1 (-)
Fig. 11. RS485-1 three-position slide switch setting MID
BIAS
RS485-1 (+)
RS485-1 (-)
Fig. 12. RS485-1 three-position slide switch setting BIAS
END
RS485-1 (+)
RS485-1 (-)
Fig. 13. RS485-1 three-position slide switch setting END
NOTE: All terminals are protected (up to 24 Vac) against
short-circuiting and incorrect wiring – except when
the 3-position slide switch is set to "END," in which
case the terminals of the RS485-1 bus (24, 25, and
26) have no such protection. Higher voltages may
damage the device.
NOTE: According to BACnet standards, a minimum of one
and a maximum of two BACnet devices must have
its/their bias resistors switched ON. In the case of
the RS485-1 interface of the EAGLEHAWK, setting
its slide switch to either "BIAS" or "END" fulfills this
requirement.
7
+5V
ISO
47 kOHM
25
26
47 kOHM
GND-1
+5V
ISO
550 OHM
25
26
550 OHM
GND-1
+5V
ISO
550 OHM
25
150 OHM
26
550 OHM
GND-1
EN1Z-1005GE51 R0216