Eight working modes of stm32gpio and chip naming rules

One 、STM32 Chip naming rules

Two 、GPIO Eight working modes

Enter the float

Input pull-up

Type in the dropdown

Analog input

Open drain output

Push pull output

Push pull multiplexing

Open drain taking function

1、 Enter the float

Floating space , As the name suggests, floating in the air , It goes up with a rope , Below with a rope to pull down .

Floating input is usually used for external key input , Combined with the input circuit on the diagram , I understand it as floating input state ,IO The level state of is uncertain , It's all up to external input , If the pin is suspended , Reading the level of the port is uncertain .

2、 Input pull-up

 3、 Type in the dropdown

4、 Analog input

 

5、 Open drain output

 

6、 Push pull output

 

7、 Push pull multiplexing

 

8、 Open drain multiplexing function

 

Floating space , As the name suggests, floating in the air , It goes up with a rope , Below with a rope to pull down .

Open a leak , It's like the output is connected to NPN triode , And only took e,b. c extremely   It's open , You can connect a resistor to 3.3V, You can also connect a resistor to 5V, such , At output 1 When , It could be 5V voltage , It can also be 3.3V The voltage is on . But when it's not connected to the resistor pull-up , This output is too high to be realized .

Open a leak Output : The output is equivalent to the collector of triode .  To get a high level state, you need to pull up the resistor .  It is suitable for current drive , Its ability to absorb current is relatively strong ( commonly 20ma within ).
The open drain circuit has the following characteristics ：
1.  Using the driving power of external circuits , Reduce IC Internal drive . When IC Inside MOSFET Conduction time , The driving current is from the outside VCC Flow through R pull-up ,MOSFET To GND.IC Only a very low gate drive current is needed inside .
2.  Generally speaking , Open drain is used to connect devices of different levels , For matching levels , Because the open drain pin is not connected to the external pull-up resistance , Only output low level , If you need to have the function of output high level at the same time , You need to connect the pull resistance , A good advantage is by changing the voltage of the pull-up power supply , The transmission level can be changed . For example, the pull-up resistor can provide TTL/CMOS Level output, etc .（ The value of the pull-up resistor determines the speed of the edge of the logic level conversion  . The greater the resistance , The lower the speed, the lower the power consumption , So the choice of load resistance should consider both power consumption and speed .）
3. OPEN-DRAIN Provides a flexible way to output , But there are also weaknesses , It's the delay that brings the rising edge . Because the rising edge is through external pull-up passive resistance to charge the load , So when the resistance is selected, the delay is small , But the power consumption is high ; On the contrary, the delay is large and the power consumption is small . So if there is a requirement for delay , It is recommended to use the falling edge output .
4.  Multiple open drain outputs can be Pin, Connect to a line . Through a pull-up resistor , Without adding any devices , formation “ And logic ” Relationship . This is also I2C,SMBus The principle of judging the occupied state of the bus . Add ： What is? “ Line and ”？：
At a node ( Line ) On ,  Connect a pull-up resistor to the power supply  VCC  or  VDD  and  n  individual  NPN  or  NMOS  The collector of a transistor  C  Or leakage  D,  The emitters of these transistors  E  Or source  S  It's all connected to the ground ,  As long as one transistor is saturated ,  This node ( Line ) It's pulled to the ground level .  Because the base of these transistors injects current (NPN) Or grid plus high level (NMOS), The transistor will saturate ,  So these bases or gates are very important to this node ( Line ) The relationship between right and wrong  NOR  Logic .  If this node is followed by an inverter ,  It's or  OR  Logic .
In fact, it can be simply understood as ： When all the pins are connected , Connect an external pull-up resistor , If there is a pin output for logic 0, It's equivalent to grounding , A circuit in parallel with it “ It's equivalent to being short circuited by a wire ”, So the logic level of the external circuit is 0, Only for the high electricity , The result of and is logic 1.

push-pull , It's push and pull , anytime IO The level of each port is certain , No external pull-up or pull-down resistor is required .

push-pull The circuit is two triodes with the same parameters or MOSFET, Exist in the circuit in push-pull mode , They are responsible for the amplification of positive and negative half cycle waveforms , When the circuit is working , Only one of the two symmetrical power switches is on at a time , So the conduction loss is small 、 Efficient . The output can supply current to the load , You can also draw current from the load . The push-pull output stage improves the load capacity of the circuit , And increase the switching speed .

because Floating input Generally used for external key input , Combined with the input circuit on the diagram , I understand it as floating input state ,IO The level state of is uncertain , It's all up to external input , If the pin is suspended , Reading the level of the port is uncertain .
Pull up input / Drop down input / Analog input ：

First of all, the purpose of up and down is to IO Set a default state , For example, if the key control is enabled , If the key is pressed, the high level is effective , Let's pull down , Let the IO The port is at low level by default （ That is, when no key is pressed IO The port always detects a low level , Only when the key is pressed IO Eloquence will detect a high level ）; If the key is pressed, the low level is valid , Let's pull up , Let the IO The port is at high level by default （ That is, when no key is pressed IO The port always detects a high level , Only when the key is pressed IO Eloquence will detect a low level ）.

        It's a little twisted , Simplify understanding ： Is to make GPIO We know that the input pin can have a certain level signal without an input signal , Pull up is the high level （ Because the pull-up input has a resistor inside the chip, and one end is connected to VCC, Pull down is the low level （ Because the pull-down input has a resistor inside the chip, and one end is connected to GND）.

        Like here KEY0/KEY1 Key , When not pressed , Because one end is connected GND And it is disconnected , Connected at the other end GPIO The pin should be configured to detect a high-level signal by default （ Only when the key is pressed, the low-level signal is detected , That is, the low level is effective ）, So the key initialization is related IO To configure as a pull-up input ; and WK_UP Key , When not pressed , Because one end is connected VCC And it is disconnected , Connected at the other end GPIO The pin should be configured to detect a low-level signal by default （ Only when the key is pressed, the high-level signal is detected , That is, the high level is effective ）, So the key initialization is related IO To configure as a drop-down input .

        Further simplification ： Pull up input refers to IO On the mouth （ Inside the chip ） String a resistor to vcc, Normal condition IO What is monitored is high level , Suitable for external grounding GND Key input of ; Drop down input refers to IO On the mouth （ Inside the chip ） String a resistor to GND, Normal condition IO Low level is detected , Suitable for external grounding VCC Key input of .（ I really don't understand , Remember to use it ）

Reuse open drain output 、 Multiplexing push pull output ： It can be understood as GPIO The configuration when the port is used as the second function （ That is, not as a general purpose IO Mouth use ）
Finally, summarize the use of ：
stay STM32 Choose IO Pattern
（1）  Floating input _IN_FLOATING —— Floating input , You can do it KEY distinguish ,RX1
（2） With pull-up input _IPU——IO Internal pull-up resistor input
（3） With drop-down input _IPD—— IO Internal pull-down resistor input
（4）  Analog input _AIN —— application ADC Analog input , Or low power consumption
（5） 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 .

Only strong low level can be output , The high level depends on the external resistance . The output is equivalent to the collector of triode , To get a high level state, you need to pull up the resistor , It is suitable for current drive , Its ability to absorb current is relatively strong （ commonly 20ma within ）.
（6） Push pull output _OUT_PP ——IO Output 0- Pick up GND, IO Output 1 - Pick up VCC, Read input value is unknown .

It can output high and low levels , Connect digital devices .
（7） Push pull output of multiplexing function _AF_PP —— Internal and external functions （I2C Of SCL,SDA）.
（8） Open drain output of multiplexing function _AF_OD—— Internal and external functions （TX1,MOSI,MISO.SCK.SS）.