National Instruments AT-MIO-16X - Manual (Page 64)

Chapter 2 Configuration and Installation
AT-MIO-16X User Manual 2-42 © National Instruments Corporation
register in the AT-MIO-16X register set and then divided by 10. The
default value is 1 MHz into the Am9513A (10-MHz clock signal on the
AT-MIO-16X). The six internal timebase clocks can be used as
counting sources, and these clocks have a maximum skew of 75 nsec
between them. The SOURCE signal shown in Figure 2-19 represents
any of the signals applied at the SOURCE inputs, GATE inputs, or
internal timebase clocks. See Appendix C, AMD Am9513A Data Sheet,
for further details.
Specifications for signals at the GATE input are referenced to the signal
at the SOURCE input or one of the Am9513A internally generated
signals. Figure 2-19 shows the GATE signal referenced to the rising
edge of a source signal. The gate must be valid (either high or low) at
least 100 nsec 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 2-19. Similarly, the gate signal must be held for at least 10 nsec
after the rising or falling edge of a source signal for the gate to take
effect at that source edge. The gate high or low period must be at least
145 nsec in duration. 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.
Signals generated at the OUT output are referenced to the signal at the
SOURCE input or to one of the Am9513A internally generated clock
signals. Figure 2-19 shows the OUT signal referenced to the rising edge
of a source signal. Any OUT signal state changes occur within 300 nsec
after the source signal rising or falling edge.
Field Wiring Considerations
Accuracy of measurements made with the AT-MIO-16X can be
seriously affected by environmental noise if proper considerations are
not taken into account when running signal wires between signal
sources and the AT-MIO-16X board. The following recommendations
apply mainly to analog input signal routing to the AT-MIO-16X board,
although they are applicable for signal routing in general.