National Instruments NI 6601, User Manual

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Chapter 3 Signal Connections
NI 660x User Manual 3-10 ni.com
Note For NI 6602 devices, o u tp u t freq u ency on any of the pins sho u ld not exceed 40 MHz.
The maxim u m freq u ency yo u can drive at the I/O connector is affected by the capacitive
load yo u r cable presents. Yo u can achieve 40 MHz o u tp u t with a National Instr u ments 1 m
SH68-68-D1 shielded cable (capacitive load = 80 pF). At larger loads, yo u r maxim u m
o u tp u t freq u ency may be lower.
Counters
The co u nters on TIO devices are a s u perset of the DAQ system timing
controller (DAQ-STC) general-p u rpose co u nters developed by National
Instr u ments. These co u nters are backward compatible with the DAQ-STC
in f u nctionality and software programming. The same software API and
f u nctions are u sed to program the DAQ-STC general-p u rpose co u nters and
the co u nters on TIO devices.
The co u nters on TIO devices have two internal timebases: 100 kHz and
20 MHz. The co u nters on the NI 6602 and NI 6608 also have an 80 MHz
timebase. Each co u nter has a gate, a u xiliary, and so u rce inp u t. Each of
these inp u ts can be an internal or external signal that connects to the
I/O connector. Each co u nter also has an o u tp u t signal.
Counter n Source Signal
Yo u can select any PFI as well as many other internal signals as the
Co u nter n So u rce (Ctr n So u rce) signal. The Ctr n So u rce signal is config u red
in edge-detection mode on either the rising or falling edge. The selected
edge of the Ctr
n So u rce signal increments and decrements the co u nter val u e
depending on the application the co u nter is performing.
Yo u can export the Ctr n So u rce signal to the I/O connector’s defa u lt PFI
inp u t for each Ctr n So u rce. For example, yo u can export the Ctr0So u rce
signal to the PFI 39/CTR 0 SRC pin, even if another PFI is inp u tting
the Ctr0So u rce signal. This o u tp u t is set to high-impedance at start u p.
For most applications, u nless yo u select an external so u rce, the
80MHzTimebase signal (if available), 20MHzTimebase signal,
or 100kHzTimebase signal generates the Ctr
n So u rce signal.