Product Overview
1-19
High Speed Counter Encoder Module User Manual
The
retriggerable one-shot mode generates an output that is On (high), from
the first clock after a trigger
, and remains On until the preset number of
clocks have been counted down to zero. The output is On for the preset
number of clocks.
See Figure 1-13. T
wenty is an arbitrary starting count value. The
waveforms show that the first clock pulse after the trigger transitions the
output On (high), and the counter counts down from the preset value (2).
When the counter reaches zero, the output goes Off. The count value
continues to decrement, and the output remains Off even through a rollover
to the preset value.
If the input clock starts Off (low) after the trigger
, the first rising edge
decrements the count value without loading the preset value. The next
clock, which is a On-to-Off-to-On clock pulse, reloads the preset value.
A trigger is required to repeat the cycle. The output remains Off until the
next clock after the next trigger which reloads the preset and starts the
count again. The last clock decrements the count to zero and turns the
output Off. If a trigger does not occur
, the count value continues to
decrement, and the output remains Off even through a rollover to the preset
value.
A trigger can be either, an external input, or the PLC can set the
corresponding Reset Counter flag, WY19.03, .04, .07, .08 for counter [2, 3, 5,
or 6]. In this example, the preset value is 2.
Pulse
Input
Starts Of
f
Trigger
, Reset, or
Programming
Output
Starts On
20 2 1 0 –1 –2 –3 –4 2 120 0 –1 –2 –3 –4
20 2 1 0 –1 –2 –3 –4 2 119 0 –1 –2 –3 –4
Figure 1-13 Retriggerable
One-Shot Mode
Retriggerable
One-Shot
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