Honeywell Centra Line EAGLE Installation & Commissioning Instructions page 7

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 EAGLE – see Fig. 11 and
Table 5; it also depends upon the selected communication
protocol (BACnet MS/TP or Panel Bus, respectively).
Table 5. Recommended slide switch settings
setting
Controllers located on both ends of bus should have
END
this setting.
In small bus networks, one controller should have this
BIAS
setting.
All other controllers (not set to "END" or "BIAS") on
MID
bus should have this setting (which is the default).
MID (DEFAULT)
RS485-1 (+)
RS485-1 (-)
Fig. 11. RS485-1 three-position slide switch setting MID
EAGLE CONTROLLER – INSTALLATION & COMMISSIONING INSTRUCTIONS
RS485-1
location / usage
+5V
ISO
47 kOHM
47 kOHM
GND-1
BIAS
Fig. 12. RS485-1 three-position slide switch setting BIAS
END
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, at least one BACnet
device must have its bias resistors switched ON, and
at most two BACnet devices may have their bias
resistors switched ON.
25
RS485-2 Bias and Termination Resistors
RS485-2 is not equipped with a slide switch. The 550Ω bias
resistors and 130Ω termination resistor of the RS485-2 are
26
thus always ON.
7
+5V
ISO
550 OHM
RS485-1 (+)
RS485-1 (-)
550 OHM
GND-1
+5V
ISO
550 OHM
RS485-1 (+)
150 OHM
RS485-1 (-)
550 OHM
GND-1
EN1Z-0970GE51 R1112
25
26
25
26