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IO821: Precision timing I/O module with optional GNSS

Precision timing module with IRIG and 1PPS interfaces and optional GNSS (GPS, GLONASS,...)

The IO821 I/O module - with 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 5ns 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.



  • Input and output 1PPS interfaces
  • Output accuracy: UTC ± 15ns for stationary conditions (IO821-GPS only) and UTC ± 50ns for other conditions (locked to GPS 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-GPS)


  • Inputs and outputs for both IRIG DCLS and IRIG AM
  • The IRIG inputs accept IRIG (formats A, B, G), NASA36 and IEEE 1344
  • The IRIG outputs accept IRIG (formats A, B, E, G), NASA36 and IEEE 1344

 Crystal oscillator

  • Capable of 5ns resolution
  • Disciplined by and phased-locked to external timing input
  • TCXO oscillator with IO821 variant and OCXO oscillator with IO821-GPS variant.
  • 10 MHz oscillator output

 GNSS receiver (IO821-GPS 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 & GLONASS)


I/O module Timing Sources
Timing Outputs
Crystal Oscillator
GNSS receiver









Form factor PMC
Power requirements 5 V: 7 W typical
3.3 V: 2.3 W typical
+12 V: 2.4 W typical
-12 V: 2.4 W typical
Bus PCI bus 32bit 33MHz/66MHz
Connector(s) 25-pin micro-miniature D-sub plug
Includes adapter cable with:
1) DB-9 female: IRIG DCLS Input
2) BNC female: IRIG AM input
3) BNC female: IRIG AM output
4) BNC female: 1PPS input
5) BNC connector: 1PPS output
Crystal oscillator
Resolution 5 ns
Phase-locked Disciplined by and phased-locked to external timing input
Type TCXO (default)
OCXO (-GPS option) for extended holdover accuracy
Accuracy 1x10-11 (TCXO)
5x10-12 (OCXO)
Medium term stability 1x10-8 / day for TCXO
2x10-9 for OCXO (-GPS option)
(both without CPS after 2 weeks of GNSS lock)
Output 10-MHz sine wave (50 Ohm output impedance)
Timing inputs
External 1PPS input • 1 Hz pulse, rising edge active
• Minimum pulse width of 100 nsec.
• 0 V to + 5.5 V input range
• Input impedance < 150 pF capacitance
IRIG AM Input • Accepts IRIG (formats A, B, G), NASA36 and IEEE 1344 pulse width codes
• Input stability: better than 100 ppm
• Amplitude: 500 mVp-p to 10 Vp-p
• Modulation ratio: 2:1 minimum, 6:1 maximum
• Input impedance: 10k-ohm minimum
• DC Common Mode Voltage: +/- 150 Vdc maximum
IRIG DCLS Input • Accepts IRIG (A, B, G formats), NASA36, IEEE 1344 pulse width codes
• RS-485 differential input: -7 V to +12 V common mode voltage input range, 200 mVp-p differential voltage threshold
• Single ended input
Timing outputs
1PPS • 1 Hz pulse with 200 ms pulse width
• Rise time < 10 nsec
• Signal level: TTL compatible
• Accuracy: positive edge within ± 50 nsec of UTC when locked to a valid 1PPS input reference or GPS
• Holdover after 4 hours: 12 µs (TCXO) or 3 µs (OCXO)
• Holdover after 24 hours: 450 µs (TCXO) or 100 µs (OCXO)
IRIG AM Output • Output formats A, B, E (100 Hz, 1 KHz), G; NASA36; IEEE 1344
• Amplitude 0.5 Vp-p to 6 Vp-p into 50 ohms
IRIG DCLS Output • Output formats A, B, E (100 Hz, 1 KHz), G; NASA36; IEEE 1344
• RS-485 differential signal
• Single ended amplitude
GNSS receiver
Channels 72-channel with concurrent dual-constellation reception
GNSS support GPS, QZSS, GLONASS and BeiDou
Acquisition times 26 s for cold start (GPS & GLONASS)
Operating temperature -40°C to +80°C
Relative humidity 95% at 60°C for 5 cycles of 48 hours/cycle
Radiated field immunity (RFI) EN61000-4-3 (2002): Radiated Electric Field Immunity
Electromagnetic interference immunity (EMI) EN61000-3-2 (2000): Harmonic Current Emissions
EN61000-3-3 (2002): Voltage Fluctuations and Flicker in Low Voltage
EN61000-4-2 (2001): Electrostatic Discharge Immunity
EN61000-4-5 (2001): High Voltage Surge Immunity
EN61000-4-6 (2003): RF Common Mode Immunity
EN61000-4-11 (2004): Voltage Dip and Interrupt Immunity
Electric fast transient immunity (EFT) EN61000-4-4 (2004): Electric Fast Transit Burst Immunity
Safety EN-60950-1:2006/A1:2010 Safety of Information Technology Equipment
Certification RoHS, CE, FCC Class A
I/O Access
Front IRIG AM (input and output)
IRIG DCLS (input and output)
1PPS (input and output)
10 MHz sinusoidal output
Rear -
Item ID Product Name Components
2A821X IO821
  • IO821
  • Breakout cable
  • Driver block library for Simulink Real-Time
  • Installation into real-time target machine
2B821X IO821-GPS
  • IO821 with high-precision OCXO and GNSS receiver
  • Breakout cable
  • Driver block library for Simulink Real-Time
  • Installation into real-time target machine
350100 GNSS Outdoor Antenna GPS/GNSS Outdoor Antenna supporting GPS L1, GLONASS L1, BeiDou B1, Galileo E1, and QZSS L1, with L-bracket for vent pipe/pole mounting via metal straps (included).
350101 GPS Antenna Surge Protector GPS Surge protector, highly recommended for all outdoor GPS antenna installations. Includes MP10-0000-0002 Mounting Bracket. Compatible with cable with Type N connectors.
350102 Low Loss Antenna Cable GPS 10 ft. Coax Antenna Cable Terminated With Type N Connectors.

Key to X in Item ID
Please replace the X with the code number of the specific target machine into which this I/O module shall be installed:

  • 5 = Mobile real-time target machine
  • 6 = Performance real-time target machine
  • 8 = Baseline real-time target machine

Pricing information
We don't publish pricing information on our website. Upon request by e-mail or phone we can provide a complete price list covering our entire product portfolio in various currencies. We recommend that you get in touch with us to discuss your specific needs. We can then quickly provide you with a tailored quotation including technical and pricing information.


Included in delivery

  • I/O module installed into real-time target machine
  • Adapter cable
  • Simulink driver blocks
  • Test models
  • Comprehensive documentation

Supported target machines