Are Pull-up Resistors Needed on Push-Pull Buses?

What is Pull Up and Pull Down Resistor and Where to Use them?

Internal pull-up resistors are insufficient for I2C

Pull-up resistor - Wikipedia

Does input via optocoupler need a pullup resistor ? - General Electronics - Arduino Forum

Working of Pull-up and Pull-down Resistors with Examples

Is pull up resistor mandatory for I2C? - Electrical Engineering Stack Exchange

Pull up resistors on UART - Electrical Engineering Stack Exchange

Do you actually need external resistors for a switch connecting an IO pin to ground? - Quora

Can Pull-up Resistors Be Used on SPI Lines?

SPI Basics — Rheingold Heavy

Pull-up Resistor vs Pull-down - Differences, Arduino Guide - Latest Open Tech From Seeed

Pull-up vs Pull-down resistors – Robocraze

SPI Basics — Rheingold Heavy

Practical guide to Bus Pirate pull-up resistors - DP

Open Collector NOT gates - Why do we need pull-up resistors?