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External NMEA GNSS

GNSS receivers that output NMEA ascii protocol can be used to aid the IMX EKF.

Configure IMX for NMEA GNSS Input

  1. Set serial port baudrate, matching DID_FLASH_CONFIG.serXBaudRate.

  2. Configure GPS1 using EvalTool GPS Setting tab or the DID_FLASH_CONFIG.ioConfig.

    EvalTool GPS NMEA

    DID_FLASH_CONFIG Value
    ioConfig (firmware >=1.8.5) 0x00840040

  3. Enable the NMEA messages on the external GNSS:

    Message Description
    GNS GNSS Fix data (preferred) or GGA - Global positioning System Fix Data.
    ZDA UTC time and date.
    RMC Recommended Minimum Specific GNSS Data.
    GSA GNSS DOP and Active Satellites.

  4. If RTK positioning is supported by the NMEA receiver, Enable RTK rover mode by selecting Precision Position External. This will run the INS kalman filter in high accuracy mode and forward any RTK base station corrections to the external GNSS receiver.

    DID_FLASH_CONFIG Value
    RTKCfgBits 0x00000002

Electrical Interface

The external NMEA GNSS receiver can be connected to Serial 0, Serial 1, and Serial 2 ports (3.3V TTL UART) on the IMX. See the PCB Module hardware page for a description of the IMX pinout. Serial 0 and 2 can be accessed on the main connector of Rugged-1 and Rugged-2 and all serial ports can be accessed on header H7 of the EVB-2.

Enabling NMEA on ZED-F9P

The recommended procotol with the IMX and ZED-F9P receiver is the uBlox binary protocol. However, the ZED-F9 can operate using NMEA protocol if necessary. The following steps can be used to enable NMEA protocol output on the ublox ZED-F9P receiver.

  1. Enable NMEA output using the u-blox u-center application.
    • Set the configuration: (ublox u-center menu -> View -> Configuration View) change the following. You must press the "Send" button to apply each change.
      • PRT (Ports) - Set Baudrate to match the GPS port baudrate (i.e. ser1BaudRate 921600)
      • PRT (Ports) - Enable NMEA on the connected port/UART
      • PRT (Ports) - Enable RTCM3 on the connected port/UART if using RTK
      • RATE (Rates) - Measurement Period: 200ms
      • RATE (Rates) - Navigation Rate: 1cyc
      • MSG (Messages) - Enable NMEA messages listed above for the connected port/UART (i.e. UART1 On)
        • F0-0D NMEA GxGNS
        • F0-08 NMEA GxZDA
        • F0-04 NMEA GxRMC
        • F0-03 NMEA GxGSV
    • Save the configuration: Send the CFG (Configuration) to 1 - FLASH or press the "Save Config" button with the small gear save icon (or menu Receiver -> Action -> Save Config).