Setup PPS synchronization

This tutorial explains how to setup PPS synchronization with the MRU Marine or MRU Compact. It covers the following steps:

• Pinout overview: Displays the pinout diagrams for each MRU Marine and MRU compact.

• Connect GPS to MRU: Instructions for connecting the GPS to the MRU.

• Configure MRU and verify PPS: How to configure the MRU and verify PPS synchronization using the MRU configurator.

MRU pinout overview

Overview of the pinout diagrams for MRU Marine and MRU Compact.

MRU Marine signal diagram

For more information about the electrical interface of the MRU Marine, see here.

MRU Compact RJ50 signal diagram

For more information about the electrical interface of the MRU Compact, see here.

Connect GPS to the MRU

To connect the GPS to the MRU, do the following:

• 1. Connect the PPS signal from the GPS to the signal Sync1 (PPS)

• 2. Connect the RS232 Tx signal from the GPS to the signal RX (RS232 GPS)

• 3. Connect the RS232 GND signal from the GPS to the signal GND

Configure MRU and verify PPS

Configure MRU for PPS

• Open the MRU configurator and connect to your MRU.

• Click “Settings“ -> “Input & Output“ in the left bar

• Under the RS 232 section, find port settings and click “Edit“

• Verify that UART from GPS (RS-232 port settings) is correctly configured. Default values should be used:

  • Baudrate: 115200

  • Data bits: 8

  • Parity: No parity

  • Stop bits: 1

  • Flow Control: None

• Select PPS signal as synchronization method

• Choose either Falling edge or Rising edge as PPS polarity

• Choose Offset (e.g., 100 ms) and Precision (e.g., 0.01 s)

• Click “Save“

Verify PPS synchronization

To verify PPS synchronization, do the following:

• Click “Data“ in the left bar

• In the data section, click “Stream data“

• Click on the Health section

• If a valid PPS signal is received, status bit number 5 (SYSTEM_CLOCK_SYNC) is 1 (green).

  • Note: If the PPS signal and at least one ZDA message is not received by the MRU, the SYSTEM_CLOCK_SYNC will be 0 (red).

Output protocol with status bits

To view the health status, you need to select an output protocol with MRU status bits included (e.g., NORSUB7). For more details, see here.

Select PPS synchronized timestamp

When PPS is enabled and functioning correctly, the epoch timestamps are synchronized with the reference GPS time and PPS pulse. For example, the posix timestamp output (output variable 506) is synchronized to the GPS time. Note that you can also output the variables TimeLastPPS (output variable 517) and NoLostPPS (output variable 518), which are the milliseconds since the last valid PPS pulse and the number of PPS pulses lost since synchronization with the ZDA message for absolute time. There is also a PPS variable (output variable 516) that goes from 0 to 1 if the GPS and PPS signal is correctly connected and read by the MRU. An overview of the PPS-related output variables can be seen below.