Data Hacking

240 Part III — Data Hacking
FIGURE 10-27: Hardware pulse option
Clicking the PPS Settings button also uncovers useful settings (see Figure 10-28). Use the PPS
Settings dialog box to select the hardware line to be used as the 1PPS input (DSR or CTS).
You can also set the trigger polarity:
Trigger on High to Low Transition: Causes the time to be set on a high to low transition
of the 1PPS input
Trigger on Low to High Transition: Causes the time to be set on a low to high transition
of the 1PPS input
Trigger on Any Transition: Causes the time to be set on any transition
FIGURE 10-28: PPS Settings dialog box
Sometimes, there may be a slight delay between the time a GPS receiver sends its timing information
to the computer and the time the computer receives it. Back in the Properties dialog box,
you can factor in this delay using the GPS Time Fix-up Delay value, adjusting the time ahead
or behind in milliseconds when setting the system time. The allowable values are from –999ms
to 999ms, set as follows: