Detailed explanation of GPIO input and output

GPIO Detailed explanation of input and output of

1. The difference between pull-up resistance ：

Pull up resistance ： Send an uncertain signal （ High or low level ）, Connected to the power supply through a resistor VCC Connected to a , Fixed at high level .

Pull down resistance ： Send an uncertain signal （ High or low level ）, Through a resistor to ground GND Connected to a , Fixed at low level .

Common ground ： Is to determine the high and low level of the signal , Prevent the existence of uncertain signals in digital circuits .

2. Input mode ：

1. Input pull-up (GPIO_Mode_IPU)

Here's the picture ： The signal input is pulled up and then triggered ( schmidt ) Convert to a digital signal 0、1 Read the level .

2. Type in the dropdown (GPIO_Mode_IPD)

Here's the picture ： The signal input is pulled down and then triggered ( schmidt ) Convert to a digital signal 0、1 Read the level .

3. Analog input (GPIO_Mode_AIN)

Here's the picture : Mainly used for ADC/DAC Signal processing and use , There is no need to go through the pull-down resistance or the trigger .

4. Enter the float (GPIO_Mode_IN_FLOATING)

Here's the picture ： Mainly used for IIC,USART Communication protocol , Without going through the pull-down resistance , But after the trigger

3. Output mode ：

1. Open drain output (GPIO_Mode_Out_OD)

Here's the picture ： It is generally used in the situation of level mismatch , It needs to be connected with pull resistance , When the output is high, it will pass through the inverter , To N-MOS end , The output terminal is pulled up by the pull-up resistor . When the output is low ,N-MOS Conduction , Output to ground , Output low level .

2. Open drain multiplexed output (GPIO_Mode_AF_OD)

Here's the picture ： The output of multiplexing function is directly used instead of register , It also needs to pull up the resistor , It mainly provides the second function configuration of the pin , Can be used as communication IIC etc. .

3. Push pull output (GPIO_Mode_Out_PP)

Here's the picture ： The output signal also passes through the inverter , after MOS The upper and lower parts of the tube act as output ;

When the output is high, the inverter outputs a low level ,P-MOS Conduction N-MOS end , The signal is affected by the pull-up resistance, so the output is high .

When the output is low, the inverter outputs high ,N-MOS Conduction P-MOS end , The signal is affected by the pull-down resistance, so the output is low .

4. Push pull multiplexed output (GPIO_Mode_AF_PP)

Here's the picture ： Directly use the multiplexing function to output , It is mainly used as the second function of the pin for output , The output is the same as the pull-down . Mainly used as serial port .

IO_Mode_AF_PP)**

Here's the picture ： Directly use the multiplexing function to output , It is mainly used as the second function of the pin for output , The output is the same as the pull-down . Mainly used as serial port .