Counter/Timer Overview
Counter/Timer Overview
You can use the versatile National Instruments counter/timer devices
to create a wide variety of measurement solutions, including
measuring a number of time-related quantities, counting events or
totalizing, and monitoring position with quadrature encoders.
You can also use counter/timers to generate pulses and pulse trains.
Counter/timers often fulfill critical timing functions as components
of complex measurement systems.
The NI 660x counter/timers use the NI-TIO, a National
Instruments ASIC chip specifically designed to meet the counting
and timing requirements of measurement applications that are
beyond the capabilities of off-the-shelf components. The wider
functionality and simple programming interface make the NI 660x
your best choice for counting and timing applications.
Example applications include frequency measurement, position
measurement, generation of retriggerable pulses, frequency shift-
keying, two-signal edge separation measurements, continuous
buffered event counting, and continuous buffered pulse train
measurements. The NI 660x counter/timer devices are readily
integrated into measurement systems that require synchronization
across multiple hardware devices because they are equipped with the
National Instruments PXI trigger bus or the RTSI bus. See the
counter/timer tutorial on page 789 for more information.
In addition to counter/timer functionality, the NI 660x products
include TTL/CMOS-compatible digital I/O ports that are bit
configurable for input or output.
Counter/Timer Size or Number of Bits
The counter size or number of bits indicates how high a counter can
count. For example, a 32-bit counter can count up to 2
32
-1 or
4,294,967,295 before it rolls over. A high number of bits is beneficial
in cases such as pulse width measurements where a wide dynamic
range is required. For example, if you measure pulse widths with a
12.5 ns resolution (80 MHz timebase) using a counter/timer with
32 bits, you can measure pulse widths up to 53 s [(2
32
-1) x 12.5 ns)]
with 12.5 ns resolution.
Data Acquisition and
Signal Conditioning
Maximum Source Frequency
Counter/Timer Considerations
Number of Counter/Timers
The counter/timer is a basic unit of hardware functionality on a
measurement device. The more counter/timers there are on a device,
the more counting/timing operations that device can simultaneously
perform. The number of DMA channels determines how many
buffered, high-speed operations can be simultaneously performed.
See page 393 for more information.
Maximum source frequency represents the speed of the fastest signal
the counter can count. If you use a higher source frequency, you can
achieve higher resolution. For example, an 80 MHz counter can
count pulses that are 12.5 ns (
1
⁄
80 x 10
) apart. You can use prescalers to
increase the maximum source frequency for event counting and
frequency measurement.
6
Family
NI 6601
NI 6602
NI 6608
1
Max
2
DMA
Bus
PCI
PCI
PXI
PXI
Counter/
Timers
4
8
8
Size
32 bits
32 bits
32 bits
Max Source
Frequency
20 MHz
1
80 MHz
1
80 MHz
1
Compatibility
5 V TTL/CMOS
5 V TTL/CMOS
5 V TTL/CMOS
Digital I/O
Up to 32
Up to 32
Up to 32
Pulse
Generation
✓
✓
✓
Buffered
Operations
✓
✓
✓
Debouncing/
Glitch
Oscillator
Removal
Stability
✓
50 ppm
✓
50 ppm
✓
75 ppb
GPS
Synchr.
–
–
✓
Buffered Operations
2
DMA
Interrupt
1
3
3
5
3
5
Page
388
388
388
Source Frequency with prescalers is 60 MHz for the NI 6601 and 125 MHz for the NI 6602 and NI 6608. These frequencies are dependent on drive strength of input signal and cable length. Consider these speeds to be the maximum.
transfers have higher throughput than interrupt transfers. See page 393 for detailed specifications.
386
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