Remote Signals; Discussion - Cablescan 90 Series Reference Manual

Page 26 2.0 Setup - Series 90/90HV
REMOTE SIGNALS
DISCUSSION
The Series 90 provides external control signals through a I5-pin D-type connector on the rear of
the System Controller. These signals are active during Test. They can be used to signal external
devices and equipment when a test is in progress (TESTING) and when a test is complete (END-
Of -TEST), and to indicate whether the test passed or failed (P ASSIF AIL).
When a test is started, the TESTING signal changes from a logic high state to a logic low and
remains low until the end of test. The END-Of-TEST signal transitions from a logic high state
to a logic low state when the test is complete and remains low for approximately 15 ms. After 15
ms, END-Of-TEST and TESTING signals return to a logic high state. A PASSIFAIL test status
signal is output and occurs approximately 2 ms before the END-Of-TEST transitions low. If the
test passed, the signal remains high. If the test failed, the signal transitions to a logic low.
(External circuits can use END-Of-TEST to latch PASS/fAIL test status signal.) The
PASSIFAIL output is held for approximately 2 ms after END-Of-TEST and TESTING return to
the high state. The time diagram is shown below:
TESTING
l'-____________ -'
•
END-Of-TEST •
PASS/fAIL
(Passed)
PASSIFAIL
(failed)
2ms
~
:.-
~ ~2ms
15 ms
:+-
Note: Timing is approximate and can vary between systems.
CAUTION
The output signals come from a 74HC04 and are protected with
1000 ohm isolation resistors. It is recommended to externally
buffer these signals with a suitable IC when driving devices
requiring more than a few microamps of current, such as relays.
•