Measuring GPS Timestamp
You can take a GPS timestamp measurement with the NI PXI-6608. In a GPS timestamp measurement, the NI PXI-6608 determines the precise time of year using a specialized onboard counter. You can select a single point (on-demand) timestamp or a buffered (sample clock) timestamp.
You can synchronize the GPS timestamp counter to a GPS receiver signal by using a pulse per second (PPS) or an IRIG-B (timecode TTL) synchronization signal from the GPS receiver. PPS does not include any timing information; rather, the PPS accurately reports when the beginning of a second occurs. IRIG-B, on the other hand, has the time encoded in the signal from the beginning of the current year. The GPS counter can latch on the current time upon receiving a hardware gate signal. GPS does not provide year information; however, the time is stored in a 64-bit floating-point number that can be converted to seconds since January 1 of the current year.
When doing an on-demand GPS timestamp measurement, you must first arm the counter by calling the Start function/VI. Each subsequent read returns the number of seconds counted.
When doing a buffered GPS timestamp measurement, the current time is latched on each active edge of the sample clock and stored in the buffer. There is no built-in clock for buffered GPS timestamp measurements, so you must supply an external sample clock.