Data Translation DT9800 Series, Руководство пользователя

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Principles of Operation
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In this configuration, use software to specify the counter/timer mode
as frequency measurement or event counting (count), and the
duration of the system timer over which to measure the frequency.
(The system timer uses a resolution of 1 ms.) In this configuration,
frequency is determined using the following equation:
Frequency Measurement = Number of Events
Duration of the System Timer
If you need more accuracy than the system timer provides, you can
connect a pulse of a known duration (such as a one-shot output of
another user counter) to the external gate input. Refer to the
DT9800
Series Getting Started Manual for wiring examples.
In this configuration, use software to set up the counter/timers as
follows:
1. Set up one of the counter/timers for one-shot mode, specifying
the clock source, clock frequency, gate type, type of output pulse
(high or low), and duty cycle.
2. Set up the counter/timer that will measure the frequency for
event counting mode, specifying the clock source to count, and
the gate type (this should match the pulse output type of the
counter/timer set up for one-shot mode).
3. Start both counters (events are not counted until the active period
of the one-shot pulse is generated).
4. Read the number of events counted. (Allow enough time to
ensure that the active period of the one-shot occurred and that
events have been counted.)
5. Determine the measurement period using the following
equation:
Measurement period = 1 * Active Pulse Width
Clock Frequency