Data Translation DT9840 Series, Руководство пользователя

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Principles of Operation
33
Edge Types
Note: The edge type applies only to measure mode and continuous measure mode
operations.
When measure mode, described on page 38 , or continuous measure mode, described on page
39 , is selected, you must specify the edge of the signal that starts and stops the measurement.
In measure mode, the counter increments from the specified start edge to the specified stop
edge. In continuous measure mode, the counter increments from the specified start edge to the
next start edge.
DT9840 Series modules provide the following edge types:
• Rising-edge external gate input – In measure mode, starts or stops the measurement
when the signal connected to the external gate input pin goes from low to high (rising
edge).
In continuous measure mode, starts the measurement when the signal connected to the
external gate input goes from low to high (rising edge); the measurement stops on the
next rising edge of the gate signal.
• Falling-edge external gate input – In measure mode, starts or stops the measurement
when the signal connected to the external gate input pin goes from high to low (falling
edge).
In continuous measure mode, starts the measurement when the signal connected to the
external gate input goes from high to low (falling edge); the measurement stops on the
next falling edge of the gate signal.
• Rising-edge external clock input – In measure mode, starts or stops the measurement
when the signal connected to the external C/T clock input pin goes from low to high
(rising edge).
In continuous measure mode, starts the measurement when the signal connected to the
external C/T clock input goes from low to high (rising edge); the measurement stops on
the next rising edge of the C/T clock input signal.
• Falling-edge external clock input – Starts or stops a measure mode or continuous
measure mode operation when the signal connected to the external C/T clock input pin
goes from high to low (falling edge).
In continuous measure mode, starts the measurement when the signal connected to the
external C/T clock input goes from high to low (falling edge); the measurement stops on
the next falling edge of the C/T clock input signal.
If you want to measure the frequency or period of a signal, specify the edges as one of the
following:
• Start edge = rising; Stop edge = rising
• Start edge = falling; Stop edge = falling