Data Translation DT9837, Руководство пользователя

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Principles of Operation
85
Gate Input Features
The DT9837A-OEM module provides a 4-pin gate input connector for connecting a TTL gate
input signal; see
page 133 for connector pin assignments. The DT9837B module provides a
BNC connector for connecting a gate input signal.
You can read the value of gate counter 2 to measure the time between the following signals:
• Completion of the A/D sample to the rising or falling edge of the gate input signal
• Rising or falling edge of the gate input signal to the rising or falling edge of the gate input
signal, which you can use to determine the pulse width of the gate signal
• Rising or falling edge of the gate input signal to the completion of the A/D sample
For these measurements, specify channel 6 in the analog input channel list. An internal
48 MHz clock (with 21 ns resolution) is used for the measurements, which allows you to
precisely correlate analog input data with measurements from the gate input signal.
You can specify the following parameters for gate counter 2 using the Open Layers Control
Panel applet, described on
page 36 , or by writing to the registers of the module, as described
in Appendix C starting on page 135 :
• The signal that starts the measurement: A/D sample, gate rising edge, or gate falling edge
• The signal that stops the measurement: A/D sample, gate rising edge, or gate falling edge
Note: Note that if you choose to start the measurement using the A/D sample, choose a
gate input edge to stop the measurement. Likewise, if you choose to stop the
measurement using the A/D sample, choose a gate input edge to start the measurement.
If you choose the start and stop the measurement using the same gate edge, be aware that
the stopping edge does not restart the measurement; the next starting edge will start the
next measurement.
• The value of the Self-Clear flag, which determines the value that is read between
measurements (either 0 or the previous measurement value)