S-COM 7K, Руководство пользователя, Страница: 362 / 400

7K
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Appendix C
C-4
above and below this 2V threshold as the incoming carrier is applied and
removed.
The third resistor mentioned above is R12 (4.7K), which is a “pullup” resistor
connected between the input pin and the controller’s +5V supply. The purpose
of the pullup resistor is to provide input current for the transistor in installations
using dry contacts, or an open- collector transistor driver, to feed the COR
input.
The purpose of the voltage divider mentioned above is to increase the
threshold of voltage needed to switch the input ON and OFF. If the divider were
not used, the input threshold would be only 0.7V, and some COR drivers would
keep the input “high” permanently.
•
If your receiver’s COR circuit provides a pair of relay contacts to indicate
carrier detection, connect one contact to the COR input of the controller and
the other contact to ground.
•
If your COR circuit provides and open-collector transistor (or open-drain
MOSFET), connect the signal to the COR input.
•
If, however, your COR circuit sources a voltage (such as from a TTL logic
gate or an op amp comparator circuit), you may need to disable the
controller’s input.
To check your installation:
•
Make the connection.
•
Measure the voltage at the controller’s COR input pin with both the
controller and receiver powered up.
•
The voltage should swing above and below the 2V threshold as an
incoming carrier is applied and removed.
Some COR drivers have low output impedances, and it is not necessary to clip
the pullup resistor. However, if the pullup resistor interferes with the operation
of your COR driver, you should clip one lead and lift the resistor to prevent it
making contact.
Finally, determine the “sense” of your receiver’s COR signal. That is, does the
COR signal go
low
or
high
when an incoming carrier is detected?
•
If the COR goes low when a carrier is applied and returns high when the
carrier is removed, place DIP Switch #1 (part of S2) in the ON (closed)
position.
•
If, however, the COR goes high when a carrier is applied and returns to low
the carrier is removed, place DIP Switch #1 in the OFF (open) position.