The HI-8429 is an 8-channel discrete-to-digital sensor fabricated with Silicon-on-Insulator (SOI) technology designed to interface with a Serial Peripheral Interface (SPI).


Each input is individually configurable as either GND/Open or Supply/Open (28V/Open). Discrete input thresholds are programmable in the range of 2V to 12V. An SPI bus is used to configure the sensors and to read sensor data.


The part operates from a 3.3V (±5%) digital supply and 12V to 16.5V analog supply.


A 1mA wetting current is sourced from the input network on each SENSE input when GND/Open mode is selected for that pin. The wetting current serves to prevent dry relay or switch contacts. An optional debounce circuit also ensures sensor outputs respond correctly to mechanical sensor inputs. A sensor output interrupt pin alerts the system to a change in sensor input, avoiding constant polling via SPI to check status.


All sense inputs are internally lightning protected to RTCA/DO160G, Section 22 Level 3 Pin Injection Test Waveform Set A(3 & 4), Set B (3 & 5A) and Set Z (3 & 5B) without using external components.


Higher levels of lightning protection can be achieved with an external series resistor and transorb at each SENSE input, refer to AN305 for more details.




  • Eight discrete inputs, individually configurable as GND/Open or Supply/Open (28V/Open)
  • Sense inputs lightning protected to RTCA/DO1060G, Section 22 Level 3 Pin Injection Test Waveforms with no external components
  • 10MHz Serial Peripheral Interface (SPI) allows daisychaining of parts for efficient board routing
  • SPI programmable sensor thresholds
  • Sensor data read through SPI bus
  • Interrupt generated on any change of sensor state
  • Withstands inadvertent application of 115V AC/400 Hz power to Sense inputs.
  • Airbus ABD0100H compliant
  • MIL-STD-704 compliant
  • Internal Self-Test mode checks analog comparators and logic
  • Robust CMOS Silicon-on-Insulator (SOI) technology
  • Industrial & extended temperature ranges available



  • Avionics discrete sensing applications



ADK-8429: HI-8429 Discrete-to-Digital Sensor Evaluation Board

ADK-8429: HI-8429 Discrete-to-Digital Sensor Evaluation Board

The Holt HI-8429 Evaluation Board demonstrates the features of the HI-8429, an 8-channel Ground/Open or 28V/Open discrete-to-digital sensor IC with SPI interface. The HI-8429 is powered from 3.3V ± 5% VLOGIC and 12 to 16.5V VDD supply voltages. The device is configured and sensor data read by the SPI serial bus. Sensor input thresholds and hysteresis are programmed via the SPI bus by writing to the four on-chip DACs. The EVM (Evaluation Module) contains a 16-bit, Freescale MC9S12XDT512 MCU, which is used to interface to a terminal emulator and control the device.
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