National Instruments E Series - Manual (Page 79)

Chapter 4 Signal Connections
 National Instruments Corporation 4-43 DAQCard E Series User Manual
DAQCard. Figure 4-30 shows the GATE signal referenced to the rising
edge of a source signal. The gate must be valid (either high or low) for
at least 10 ns before the rising or falling edge of a source signal for the
gate to take effect at that source edge, as shown by t
gsu
and t
gh
in
Figure 4-30. The gate signal is not required to be held after the active
edge of the source signal.
If an internal timebase clock is used, the gate signal cannot be
synchronized 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 DAQCards. Figure 4-30 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
FREQ_OUT signal is the output of the DAQCard frequency generator.
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 signal is set
to input (High-Z) at startup.