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Chapter 4
Signal Connections
©
National Instruments Corporation
4-23
6711/6713/6715 User Manual
Figure 4-17. The gate signal is not required to be held after the active edge
of the source signal.
If you use an internal timebase clock, you cannot synchronize the gate
signal with the clock. In this case, gates applied close to a source edge take
effect either on that source edge or on the next one. This arrangement
results in an uncertainty of one source clock period with respect to
unsynchronized gating sources.
The OUT output timing parameters are referenced to the signal at the
SOURCE input or to one of the internally generated clock signals on the
671X device. Figure 4-17 shows the OUT signal referenced to the rising
edge of a source signal. Any OUT signal state changes occur within 80 ns
after the rising or falling edge of the source signal.
FREQ_OUT Signal
This signal is available only as an output on the FREQ_OUT pin. The
frequency generator for the 671X device outputs the FREQ_OUT pin. The
frequency generator is a 4-bit counter that can divide its input clock by the
numbers 1 through 16. The input clock of the frequency generator is
software-selectable from the internal 10 MHz and 100 kHz timebases. The
output polarity is software selectable. This output is set to tri-state at
startup.
Field Wiring Considerations
The following recommendations apply for all signal connections to the
671X device:
•
Separate the 671X device signal lines from high-current or
high-voltage lines. These lines can induce currents in or voltages on
the 671X device signal lines if they run in parallel paths at a close
distance. To reduce the magnetic coupling between lines, separate
them by a reasonable distance if they run in parallel, or run the lines at
right angles to each other.
•
Do not run signal lines through conduits that also contain power lines.
•
Protect signal lines from magnetic fields caused by electric motors,
welding equipment, breakers, or transformers by running them through
special metal conduits.
For more information, refer to the application note, Field Wiring and Noise
Consideration for Analog Signals, available from National Instruments.
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