SAFETY IN I/O
(pagina padre — versione finale, pronta per il workspace)
Introduction
I/O interfaces form the physical boundary between the chip and the external world. Because they interact directly with sensors, actuators, communication lines, and power domains, they represent one of the most critical points of failure in safety‑related systems.
This page introduces the safety principles that apply to both digital and analog I/O, and serves as the parent for the two dedicated subpages.
Figure 1: I/O Safety Context Map.
High‑level overview of the safety‑relevant elements along the I/O boundary: external world → I/O pins → interface logic → diagnostic mechanisms → safety architecture → system core. The diagram highlights where faults originate and where safety mechanisms operate.
Why I/O Safety Matters
Faults at the I/O boundary can propagate directly into the physical environment, causing incorrect actuation, invalid sensing, or hazardous system behavior.
Typical risks include:
- incorrect actuator control
- invalid sensor readings
- short circuits and electrical overstress
- loss of communication integrity
- unsafe fallback behavior
Ensuring safe operation requires fault detection, plausibility checks, and robust fallback strategies.
Failure Categories
I/O faults can be grouped into two major families:
Digital I/O faults
- stuck‑high / stuck‑low
- open pin
- short‑to‑ground
- short‑to‑battery
- bridging faults
Analog I/O faults
- sensor open / short
- drift and offset
- saturation
- reference mismatch
- noise injection
Each family requires different diagnostic mechanisms and architectural protections.
Diagnostic Mechanisms
Safety‑critical systems rely on multiple layers of diagnostics:
- boundary scan for pin‑level testing
- read‑back and loopback paths
- current sensing and short detection
- plausibility checks and redundancy
- ADC/DAC self‑test and reference monitoring
- FCCU integration for centralized fault reporting
These mechanisms ensure that faults are detected promptly and that the system can transition to a safe state.
Subpages
Queste due pagine approfondiscono i meccanismi di sicurezza specifici per ciascuna categoria di I/O:
Safety in Digital I/O
Failure modes: stuck‑high, stuck‑low, open, short‑to‑ground, short‑to‑battery, bridging. Diagnostics: boundary scan, read‑back, current sensing, plausibility checks.
Safety in Analog I/O
Failure modes: sensor open/short, drift, ADC saturation, reference mismatch, noise. Diagnostics: redundant sensing, plausibility checks, reference monitoring, ADC self‑test.
Safety Architecture Considerations
I/O safety interacts with:
- FCCU for centralized fault reporting
- safe‑state management for actuators and sensors
- watchdog supervision
- protocol layers for communication integrity
- power management for voltage anomaly detection
(placeholder — diagrams, examples, I/O fault trees)
