User Defined Pulses or Programmable pulses are a common timing signal which is supplied by almost all GPS clocks. Programmable pulses are a logic high (or low) pulse that has a programmable period and duration. These pulses can range from 1000 pulses per second to one pulse per second, minute, hour, day and so on. Most equipment that use pulses will require a pulse per second (PPS) with a duration of 100 ms.
PPS signals are used to increase the accuracy of other timing protocols such as SNTP/NTP and ASCII strings, as they align the equipment’s internal counter with the on time point of the new second or the starting point of the new second. These pulses contain no time or date data.
Transmitted via fibre or STP, pulses are generally highly accurate, with most leaving the clock’s port with an accuracy of < 100 ns to UTC. Commonly, pulses are a 5 Vdc signal, but can range up to 24 Vdc depending on the application. Pulses are still widely used today and act as a common reference for many pieces of equipment.