Add GPS timing to legacy (pre-GPS) systems!
Eliminate clock drift for systems with free-running clocks by adding a GPS-NS timing card. If your legacy system has serial and digital input ports and a timer, you can upgrade your timing to GPS with a software-only solution. Simply connect the GPS-NS NMEA output to your serial port and the GPS-NS PPS output to the digital input port which controls a counter. The counter's counts is the time offset from the second (X.00000) and NMEA RMC is the time of that second. With these two numbers the time is determined to the resolution of the counter. For example, if the counter is clocked at 1 MHz, then the time is accurate to one microsecond.