Issue link: https://resources.pcb.cadence.com/i/1541046
2. Preventing Floating or Unused Inputs and Outputs How To Implement 1. Consult the datasheet for every IC: f Most datasheets specify how to handle unused inputs, outputs, analog pins, and configuration pads. f Document the recommended termination or tie-off for each unused function. 2. Terminate all unused digital inputs: f Tie unused logic inputs to a valid high or low level (VCC or GND) as appropriate; use direct connection, pull-up, or pull-down resistor per datasheet. f For open-drain/open-collector inputs, use pull-ups as specified. f Do not leave any CMOS, TTL, or Schmitt-trigger inputs floating. 3. Handle unused outputs and bidirectional pins: f For unused outputs, configure in a benign state (tri-state, pulled low/high, or disabled) if possible. f For bidirectional or bus pins (e.g., I2C, SPI, unused data lines), tie to default levels or terminate per interface guidelines. f For analog ICs (op amps, comparators), tie unused inputs to a defined voltage within the common-mode range, and configure outputs as open or driven low/high. 4. Mark and document all unused pins in the schematic: f Add a note for every NC (no-connect) or unused pin, use a unique net name (e.g., UNUSED1) for traceability. Some schematic solutions include specialized symbols representing no connects. f For programmable devices, include notes in the firmware/ config to set the pin direction and default state on startup. 5. Use appropriate resistor values for termination: f Typical pull-up/pull-down values are 1 kΩ to 100 kΩ — consult datasheet and consider power consumption vs noise immunity. 6. Double-check after each revision: f Revisit all IC pin lists after changes in the schematic or netlist — unused pins can appear or disappear during edits. Common Pitfalls, Their Impact, and How to Avoid Them Common Pitfall How to Avoid it Assuming "NC" means "leave floating" Some pins marked "NC" may need to be tied off or must not be connected — Always check datasheet. Leaving analog inputs open Exposes the node to noise pickup and undefined behavior – Provide a defined bias/termination, such as pull-up/pull-down. Not documenting unused pins This can lead to confusion or incorrect assembly or debug actions – Create an "Unused Pins" table in the schematic/fab notes and document the required state (NC, tie to GND/VDD, leave for test). Forgetting program- mable device pin direction defaults Some pins power up as inputs or outputs by default — Review power-up I/O defaults in the datasheet/user guide and configure as required.