Clamp diode working principle: using the diode is the guide and conduction voltage drop, to control the input voltage to 0.7 ~ 3.7 V, which have such effects on input, thus protecting the follow-up device,
The definition of high impedance state:
Digital circuit common terminology, refers to a state of the input of the circuit, is neither high nor low level, if the high impedance state to enter the next level circuit, the circuit without any effect at a lower level, and didn't answer, if the multimeter test is likely to be high level it is possible that the low level, followed by things along with it,
Personal understanding: high resistance state that is in unstable state between the two extremes 0, 1, between 0 ~ 1, floating in a high impedance state, with the multimeter to measure, may be a while for high, for a moment to be low, the need to stabilize some input devices, high impedance state can be considered as open circuit, the equivalent of no input, high impedance state in a certain sense enriched potential level, after all, only 1 s and 0 s in the world is so boring ah