Voltage Levels
A GPIO input does not treat every voltage as valid HIGH or LOW. The MCU datasheet defines input thresholds and output voltage characteristics.
CORE IDEA
VIH defines an acceptable HIGH input
ENGINEERING VIEW
VIL defines an acceptable LOW input
WHAT TO CHECK
VOH and VOL describe output behavior
REMEMBER
Logic compatibility must be checked between devices
Engineer’s checklist
- VIH defines an acceptable HIGH input
- VIL defines an acceptable LOW input
- VOH and VOL describe output behavior
- Logic compatibility must be checked between devices
KEY TAKEAWAY
Digital behavior is physical behavior. When firmware and expectations disagree, measure the signal instead of guessing.