Physical / electrical concepts

Pull-up / pull-down resistor

A resistor that holds a pin at a known voltage (high or low) when nothing else is driving it.

How it looks

Real image: the CORE3588 schematic, exported by KiCad (shown in greys)

Real pull-ups on CORE3588, from our schematic: the I2C control wires of camera 0. Each of the six cameras has a pair like this.

1R14, 2.2 kilohm: pulls the camera's data wire CAM0_SDA up to 1.8 V when nobody pulls it down.
2R15, 2.2 kilohm: the same for the clock wire CAM0_SCL.
3VCC_1V8_S0: the 1.8 V supply both resistors pull up to.

Real image: CORE3588, rendered by KiCad from our board file

The same two resistors on CORE3588, top side, 5 x 3.6 mm.

Needed for every open-drain line, such as I2C. The resistor value and the wire capacitance set how fast the line rises: the RC time constant.