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IO821 — Precision timing module with IRIG and 1PPS interfaces and optional GNSS


The IO821 I/O module - with an optional GNSS (GPS/GLONASS) receiver – provides precision timing and synchronization for real-time applications and includes both input and output interfaces to IRIG and 1PPS. The precision timing reference uses an onboard oscillator with a 5 ns resolution that is phase-locked to an external timing reference input.

This I/O module supports multiple timing inputs and, when the current timing input is lost, it switches automatically to the next lower-priority input. Furthermore, the crystal oscillator provides uninterrupted precision timing even when all external sources become unavailable (referred to as holdover). For applications where accuracy during holdover is essential, an oven-controlled crystal oscillator (OCXO) is optionally available.

The IO821 I/O module can be used to generate an interrupt which triggers the Simulink model execution at very precise intervals. In addition, it can supply precision timing references to synchronize external hardware on the External HW Sync Output pin.


  • 1PPS

    • Input and output 1PPS interfaces

    • Output accuracy: UTC ± 15 ns for stationary conditions (IO821-GNSS only) and UTC ± 50 ns for other conditions (locked to GNSS or 1PPS source).

    • TCXO holdover accuracy: 12 μs after 4 hours and 450 μs after 24 hours (IO821)

    • OCXO holdover accuracy: 3 μs after 4 hours and 100 μs after 24 hours (IO821-GNSS)

  • IRIG

    • Inputs and outputs for both IRIG DCLS and IRIG AM

    • The IRIG inputs accept IRIG (formats A, B, G) and NASA36

    • The IRIG output supports the standard format B

  • Crystal oscillator

    • Capable of 5 ns resolution

    • Disciplined by and phased-locked to external timing input

    • TCXO oscillator with IO821 variant and OCXO oscillator with IO821-GNSS variant

    • 10 MHz oscillator output

  • GNSS receiver (IO821-GNSS only)

    • 72-channel receiver with concurrent dual-constellation reception

    • Supports GPS, QZSS, GLONASS and BeiDou.

    • Initial acquisition time of 26 s for cold start (GPS and GLONASS)

  • Edge detection inputs with timestamp

    • Two hardware inputs providing a timestamp feature

    • Rising/falling edge selectable

    • Datenum/Array output in the driver block

Driver Blocks