Chapter 3 Signal Connections
NI 660x User Manual 3-10 ni.com
Note For NI 6602 devices, output frequency on any of the pins should not exceed 40 MHz.
The maximum frequency you can drive at the I/O connector is affected by the capacitive
load your cable presents. You can achieve 40 MHz output with a National Instruments 1 m
SH68-68-D1 shielded cable (capacitive load = 80 pF). At larger loads, your maximum
output frequency may be lower.
Counters
The counters on TIO devices are a superset of the DAQ system timing
controller (DAQ-STC) general-purpose counters developed by National
Instruments. These counters are backward compatible with the DAQ-STC
in functionality and software programming. The same software API and
functions are used to program the DAQ-STC general-purpose counters and
the counters on TIO devices.
The counters on TIO devices have two internal timebases: 100 kHz and
20 MHz. The counters on the NI 6602 and NI 6608 also have an 80 MHz
timebase. Each counter has a gate, auxiliary, and source input. Each of
these inputs can be an internal or external signal that connects to the
I/O connector. Each counter also has an output signal.
Counter n Source Signal
You can select any PFI as well as many other internal signals as the
Counter n Source (CtrnSource) signal. The CtrnSource signal is configured
in edge-detection mode on either the rising or falling edge. The selected
edge of the CtrnSource signal increments and decrements the counter value
depending on the application the counter is performing.
You can export the CtrnSource signal to the I/O connector’s default PFI
input for each CtrnSource. For example, you can export the Ctr0Source
signal to the PFI 39/CTR 0 SRC pin, even if another PFI is inputting
the Ctr0Source signal. This output is set to high-impedance at startup.
For most applications, unless you select an external source, the
80MHzTimebase signal (if available), 20MHzTimebase signal,
or 100kHzTimebase signal generates the CtrnSource signal.
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