______________________________________________ Section 3: Operation
8197 Instruction Manual
Page 3-11
PIN SIGNAL
NOTES
1
+ 9.6 kHz
RS-485 B Terminal
2
+18 kHz
RS-485 B Terminal
3
+ 1 PPS
RS-485 B Terminal
4
Major Alarm
Ground = Normal
5 Ground
Cable
Shield
6
- 9.6 kHz
RS-485 A Terminal
7
-18 kHz
RS-485 A Terminal
8
- 1 PPS
RS-485 A Terminal
9 Ground
Cable
Shield
TABLE 3-3 DATA CLOCK PIN ASSIGNMENTS
The Data Clock timing signals are derived from the 10 MHz GPS disciplined
oscillator. The 1PPS and 9.6-Hz outputs are leading edge synchronized to the
GPS 1 PPS output. Using the 1PPS offset command, 1PO, the outputs can be
offset from 0 to 1 second in 0.1 microsecond steps. Refer to Section 4 for
additional information on the 1PO Command.
The 18-kHz output is not made leading edge synchronized.
3.2.4.1 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 3-8 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.