Figure 2-8 Rate Generator Mode - Keithley DAS-800 series User Manual

Rate generator (Mode 2) - This mode is useful for generating a
real-time clock interrupt. The output is initially high. A trigger loads
the initial count value into the counter. At the next clock pulse after
the trigger, the counter starts counting down. When the counter
reaches one, the output goes low for one clock pulse and then goes
high again. The counter is then reloaded with the initial count value
and the process repeats.
A high gate input enables counting; a low gate input disables
counting. If the gate goes low during an output pulse, the output is set
high immediately; this allows you to use the gate input to synchronize
the counter.
Writing a new count to the counter while counting does not affect the
current counting sequence. In this mode, a count of 1 is illegal.
Figure 2-8 illustrates rate generator mode.
Clock pulse
Output
Trigger loads initial
count value of 3
3 2
Figure 2-8. Rate Generator Mode
1 3 2 1 2
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