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 Counter/Timer Size or Number of Bits
buffered event counting, and continuous buffered pulse train The counter size or number of bits indicates how high a counter can
measurements. The NI 660x counter/timer devices are readily count. For example, a 32-bit counter can count up to 232-1 or
integrated into measurement systems that require synchronization 4,294,967,295 before it rolls over. A high number of bits is beneficial
across multiple hardware devices because they are equipped with the in cases such as pulse width measurements where a wide dynamic
National Instruments PXI trigger bus or the RTSI bus. See the range is required. For example, if you measure pulse widths with a
counter/timer tutorial on page 789 for more information.
12.5 ns resolution (80 MHz timebase) using a counter/timer with
In addition to counter/timer functionality, the NI 660x products 32 bits, you can measure pulse widths up to 53 s [(232-1) x 12.5 ns)]
include TTL/CMOS-compatible digital I/O ports that are bit with 12.5 ns resolution.
configurable for input or output.
Maximum Source Frequency
Counter/Timer Considerations
Number of Counter/Timers
Maximum source frequency represents the speed of the fastest signal
the counter can count. If you use a higher source frequency, you can
The counter/timer is a basic unit of hardware functionality on a achieve higher resolution. For example, an 80 MHz counter can
measurement device. The more counter/timers there are on a device, count pulses that are 12.5 ns (1⁄80 x 106) apart. You can use prescalers to
the more counting/timing operations that device can simultaneously increase the maximum source frequency for event counting and
perform. The number of DMA channels determines how many frequency measurement.
buffered, high-speed operations can be simultaneously performed.
See page 393 for more information.
Debouncing/
Counter/
Timers
4
8
Max Source
Frequency
20 MHz1
Pulse
Buffered
Operations
✓
Glitch
Removal
✓
Oscillator
Stability
50 ppm
GPS
Synchr.
–
–
Buffered Operations2
Family
NI 6601
NI 6602
Bus
Size
32 bits
32 bits
Compatibility
5 V TTL/CMOS
5 V TTL/CMOS
Digital I/O Generation
DMA
Interrupt
Page
388
388
PCI
PCI
PXI
PXI
Up to 32
Up to 32
✓
✓
1
3
3
5
80 MHz1
✓
✓
50 ppm
NI 6608
8
32 bits
80 MHz1
5 V TTL/CMOS
Up to 32
75 ppb
3
5
388
✓
✓
✓
✓
1Max 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.
2DMA transfers have higher throughput than interrupt transfers. See page 393 for detailed specifications.
386 National Instruments • Tel: (800) 433-3488 • Fax: (512) 683-9300 • info@ni.com • ni.com
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