High impedance (hi-Z, tri-stated, floating) means the output is not being driven to any defined logic level (neither logical high, nor low).
The use of high impedance: allow multiple circuits to share the same output line. When you enable the output (pull the line OE to low, or write to a reg), the output will drive it respective loads (0, or 1). Otherwise, it is in high-impedance.
- A pull-up resistor can be used to try to pull the wire to high and low voltage levels. When devices are inactive, they tri-state their outputs. When all the devices on the bus have done this, the pull-up resistor will pull the line up. If a dvice wants to communicate, it drives the line low.
- For non-used pins (maybe used by other component), e.g MX_CSI1_DAT(1), R10845 is NB (for pull down), R10872 is 4K7(pull up), which effectively pull up the line (3.3V).
- For pins being used: MX_CSI1_DAT(12), R10184 is 10K,
- which effectively pulls down the line when there is no signal coming;
- when the device outputs signals (drive 3.3V or 1.8V on the pin), the line will be high???