Working principle of stm32gpio port

     stm32f4 Yes 7 Group IO mouth , Each group has 16 individual IO mouth ,GPIO The pin of is connected to the external device , It can realize communication with the outside , Control external hardware , The function of collecting external hardware data , The corresponding common applications are serial port , The motor ,ADC collection .

GPIO Basic structure of port

Every GPIO There is such a circuit diagram inside the port

 

 

GPIO There are four input modes （ Floating input , Pull up input , Drop down input , Analog input ）, Four output modes （ Open drain output , Open drain multiplexed output , Push pull output , Push pull multiplex output ）.

  Besides ,GPIO In output mode, three flipping speeds are supported 2MHz,10MHz,50MHz, Without requiring fast conversion , Generally, low speed , The purpose is to save power . But in the communication protocol, we usually use 50MHz,

GPIO_Mode_AIN  Analog input
GPIO_Mode_IN_FLOATING  Floating input
GPIO_Mode_IPD  Drop down input
GPIO_Mode_IPU  Pull up input
GPIO_Mode_Out_OD  Open drain output
GPIO_Mode_Out_PP  Push pull output
GPIO_Mode_AF_OD  Reuse open drain output
GPIO_Mode_AF_PP  Multiplexing push pull output

Floating input

  Floating input mode , The external level is directly input into the data register , in other words ,IO How much level does the port input ,CPU How many levels will be read , The pin is suspended , Without signal input , The level of the read port is uncertain .

Pull up input

  In pull-up input mode ,IO The data signal of the port directly enters the data register , But without input , The input level remains high .

Drop down mode

Pull down input mode ,IO The data signal of the port directly enters the data register , But without input , The input level remains low .

Analog input

  In analog mode ,IO Analog signal of port （ Voltage signal ） Direct analog input to on-chip peripheral modules .

How to choose IO Mouth mode

Floating input _IN_FLOATING —— Floating input , You can do it KEY distinguish ,RX1
With pull-up input _IPU——IO Internal pull-up resistor input
With drop-down input _IPD—— IO Internal pull-down resistor input
Analog input _AIN —— application ADC Analog input , Or low power consumption
Open drain output _OUT_OD ——IO Output 0 Pick up GND,IO Output 1, In the air , It needs to be connected with pull resistance , In order to achieve high output level . When output is 1 when ,IO The state of the port is raised by the pull-up resistor , But because of the open drain output mode , such IO The port can also be changed from an external circuit to a low level or constant . You can read IO Input level changes , Realization C51 Of IO Two way function
Push pull output _OUT_PP ——IO Output 0- Pick up GND, IO Output 1 - Pick up VCC, Read input value is unknown
Push pull output of multiplexing function _AF_PP —— Internal and external functions （I2C Of SCL、SDA）
Open drain output of multiplexing function _AF_OD—— Internal and external functions （TX1、MOSI、MISO.SCK.SS）