User manual

Chapter 3 Software Overview

For more about

GPCTR

functions, refer to the

GPCTR_Set_Application

function description in NI-DAQ Function Reference Online Help file.

Clocks or Time Counters

NI-TIO based devices have built-in clocks, which are specialized time

counters that retrieve current time and timestamp one or more digital

triggers. The number of clocks available depends on the number of NI-TIO

chips on your device. Most devices have one clock per NI-TIO chip.

Like counters, clocks have gate signals that latch their current value,

or time. They can latch a single time or multiple times in a buffer using

interrupts or DMA. Unlike counters, clocks have additional hardware that

eliminates drift by synchronizing the clocks to a PPS or IRIG-B stream

(See Figure 3-37).

Figure 3-37.

Real-time Clock Synchronizing to a GPS Receiver

Clock Resolution

NI-TIO based clocks must have a timebase, which keeps the clock ticking.

The default timebase is the 20 MHz internal timebase. If your clock has a

20 MHz timebase, its resolution will be 50ns.

Gate

External Signal

Used for Synchronizing Other Clocks

Used for GPCTR Functionality

GPS

Satellite

Internal Timebase

Source

Synch

Satellite

Receiver

TRIG-B

PPS

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MHz 50ns=