Understanding PPS vs Programmable Pulse Output (PPO) Alignment

If the device is locked to a GPS/GNSS reference, the PPS output is explicitly aligned to GPS time. The PPS rising edge marks the top of the GPS second. Internally, PPS is generated by the device’s oscillator, which is disciplined by the active reference.

PPO outputs (including common configurations such as 1 pulse per minute) are frequency-accurate to the active reference source (for example GPS, NTP, or PTP). PPO is generated by counting time intervals between pulses. A PPO can be started on a GPS-aligned boundary, but it is not continuously phase-locked to absolute GPS time-of-week boundaries.

There is no configuration option that guarantees a PPO rising edge remains aligned to absolute GPS time-of-week minute boundaries during continuous operation. Small phase differences can accumulate over time.

• If you require a pulse strictly aligned to an absolute GPS epoch, use PPS (if available).
• If you require a stable pulse rate but do not need strict alignment to absolute GPS boundaries, PPO is appropriate.

• PPS: “This edge marks the exact reference second.”
• PPO: “This pulse runs at the correct rate, but can drift relative to absolute reference boundaries over time.”