Chapter 4
Signal Connections
PCI-4451/4452/4453/4454 User Manual
4-28
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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
PCI-4451/4452. Figure 4-16 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 (PCI-4451/4452 Only)
This signal is available only as an output on the FREQ_OUT pin. The
PCI-4451/4452 frequency generator 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 high-impedance
at startup.
Field Wiring Considerations
•
Environmental noise can affect the accuracy of measurements made
with your PCI-445X if you do not take proper care when running signal
wires between signal sources and the device. For more information,
refer to National Instruments Application Note 025, Field Wiring and
Noise Considerations for Analog Signals
The following recommendations apply mainly to analog input signal
routing to the device, although they also apply to signal routing in general.
Minimize noise pickup and maximize measurement accuracy by taking the
following precautions:
•
Route signals to the device carefully. Keep cabling away from noise
sources. The most common noise source in a PCI data acquisition
system is the video monitor. Separate the monitor from the analog
signals as much as possible.
•
Separate PCI-445X signal lines from high-current or high-voltage
lines. These lines can induce currents in or voltages on the PCI-445X
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.
