8194B, 8195B, 8197B
Spectracom Corporation
GPS Ageless Master Oscillator Instruction Manual
3-18
3.3.7.1 RS-485
Outputs
RS-485 is a balanced differential transmission requiring twisted pair cable. Cable
lengths up to 4000 feet are possible when using cables specifically designed for RS-485
applications, like Belden 9844 or equivalent. These cables have a braided shield,
nominal impedance of 120 ohms, and a capacitance of 12 to 15 picofarads per foot.
Refer to Figure 3-13 for a schematic representation of an RS-485 line driver. Relative
to RS-485 specifications the A Terminal (-) is negative with respect to the B Terminal (+)
for a Binary 1. The A Terminal (-) is positive to the B Terminal for a Binary 0.
B
A
+
-
RS-485 OUTPUT
Figure 3-13 Data Sync Drivers
3.3.8 Major Alarm Contacts
Major Alarm relay contacts are found on Pins 10, 11 and 12 of the Data Sync connector.
A Major Alarm is asserted whenever any of the following alarm conditions exist:
Frequency, Tracking Alarm 2, Tracking Alarm 3, CPU or the unit is placed in Test Mode.
During normal operation the Major Alarm relay is energized. The energized relay
causes continuity between the common contact, Pin 10 and the normally open contact,
Pin 11.
A Major Alarm or power failure de-activates the relay causing continuity between
common, Pin 10 and normally closed, Pin 12. The relay remains in alarm condition until
the fault is corrected or reset by the clear alarm, CA, command.
3.3.9 Alarm
Outputs
The Alarm Outputs connector provides relay contact closures for Major and Minor
alarms. Relay contacts are rated at 2 Amps, 30 VDC. The mating 7-position terminal
block, shown in Figure 3-14, is furnished in the ancillary kit.
