Chapter4 ConnectingSignals
©NationalInstruments Corporation 4-39 NI6013/6014 User Manual
Figure4-35. GPCTRTiming Summary
TheGATE and OUT signal transitions shownin Figure 4-35arereferenced
to the rising edge of the SOURCE signal. The assumption for this timing
diagram is that the counters are programmed to count rising edges. The
same timing diagram, but witht he source signal invertedand referenced
to the fallingedg eo f the source signal, would apply when the counter is
programmed to count falling edges.
The GATEinput timing parameters are referenced to the signal at the
SOURCE input or to one of the internally generated signals on the
NI6 013/6014. Figure 4-35 shows the GATEsignal referenced to the rising
edge of a source signal. The gate must be valid (either high or low)for at
least10 ns befo ret he rising or fallinged geo fa sourcesignalf orthe gate to
takeeffect at that source edge, as shown by tgsu and tgh in Figure 4-35.
Thegate signal is not required to be heldafter the activeedge of the source
signal.
Ifyou use aninternal timebase clock, the gate signal cannot be
synchronized with the clock. In this case, gates applied close to a source
edge takeeffect either on that source edge or on the next one. This
arrangement results in an uncertainty of one source clock period with
respectt o unsynchronized gating sources.
t
sc
t
sc
t
sp
t
sp
t
sp
V
IH
V
IL
V
IH
V
IL
V
OH
V
OL
t
gsu
t
gsu
t
gh
t
gh
t
gw
t
gw
t
out
t
out
SourceClock Period
SourcePulse Width
GateSetup Time
GateHold Time
GatePulse Width
OutputDelay Time
50ns minimum
23ns minimum
10ns minimum
0ns minimum
10ns minimum
80ns maximum
SOURCE
GATE
OUT