Counter Timing Signals; Counter Timing Summary - National Instruments 6711 User Manual

Chapter 5 Counters

Counter Timing Signals

The following sections contain information on counter timing signals.

Counter Timing Summary

Figure 5-2 shows the timing requirements for the gate and source input signals and the timing
specifications for the output signals on your device.
Figure 5-2. Gate and Source Input Timing Requirements
V
IH
SOURCE
V
IL
V
IH
GATE
V
IL
V
OH
OUT
V
OL
The gate and out signal transitions shown in Figure 5-2 are referenced to the rising edge of the
source signal. This timing diagram assumes that the counters are programmed to count rising
edges. The same timing diagram, but with the source signal inverted and referenced to the falling
edge of the source signal, applies when you program the counter to count falling edges.
The gate input timing parameters are referenced to the signal at the source input or to one of the
internally generated signals on your device. Figure 5-2 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 so the gate can take effect at that source edge, as
shown by t and t
gsu gh
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 output timing parameters are referenced to the signal at the source input or to one of the
internally generated clock signals on your device. Figure 5-2 shows the out signal referenced to
5-2 | ni.com
t
gsu
Source Clock Period
Source Pulse Width
Gate Setup Time
Gate Hold Time
Gate Pulse Width
Output Delay Time
. The gate signal is not required after the active edge of the source signal.
t
sc
t
gw
t
out
t
50 ns minimum
sc
t
10 ns minimum
sp
t
10 ns minimum
gsu
t
0 ns minimum
gh
t
10 ns minimum
gw
t
80 ns maximum
out
t t
sp sp
t
gh