What is the principle of pulling up or down when using the C6000 series pins?

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What is the principle of pulling up or down when using the C6000 series pins? [Copy link]

    The input pins of the C6000 series generally have weak pull-up or pull-down resistors inside. Generally, there is no need to consider adding pull-up or pull-down resistors externally. Special cases can be configured as needed. The microcontroller outputs a high level, but due to the influence of the subsequent circuit, the output high level is not high, that is, it cannot reach VCC, affecting the operation of the circuit. Therefore, a pull-up resistor must be connected. The situation of the pull-down resistor is the opposite. The microcontroller pin outputs a low level. As a result, due to the influence of the subsequent circuit, the output low level cannot reach GND, so a pull-down resistor is connected. When the microcontroller pin level is uncertain, let there be a stable level behind: For example, when the pull-down resistor is connected above, the level is uncertain when the microcontroller is just powered on. Also, if the microcontroller pin you connect is an input pin instead of an output pin after power-on, then the microcontroller level is also uncertain at this time. The function is to force the level to remain at a low level if the previous microcontroller pin level is uncertain.