Spectracom Corporation
Model 9289
NetClock/NTP Network Time Provider Instruction Manual
2-17
Figure 2-14: TimeBurst RS-485 Interface
2.7.6 Termination
A 120 Ohm termination resistor is required on devices located at the ends of the RS-485
transmission line. Terminating the cable end preserves data integrity by preventing signal
reflections.
For a one-way bus installation (Figure 2-8), terminate the last device on the bus. The RS-485
data bus can be split in two directions as shown in Figure 2-9. In a split bus configuration,
terminate the devices installed on each end of the bus. Some Spectracom products include a
built-in termination switch to terminate the RS-485 bus when required or a resistor is supplied
with the equipment if no termination switch is available. The terminating resistor is installed
between the positive and negative connections on the terminal block of the last RS-485
connection.
NETCLOCK
REMOTE OUTPUT
1
2
3
3-POSITION
TERMINAL BLOCK
+DATA
-DATA
GROUND
Twisted Pair
TO TIMEBURST RS-485
INPUT
+DATA
-DATA
GROUND
TO OTHER
RS-485
DEVICES
1
2
3
Summary of Contents for 9289
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