Port multiplexing and re imaging

author ： A big cat 1201
special column ：《STM32 Study 》
Maxim ： You just try to , Leave the rest to time ！

describe

Let's take a look at one STM32 Simple structure diagram of

You can see that in the diagram , Except for the kernel （ That is to say CPU）, Another part is built-in peripherals . There are many kinds of built-in peripherals , The number of built-in peripherals of different types of chips is also different , As used by benmew STM32F103ZET6 The serial port of the chip has 5 individual . These built-in peripherals are through GPIO Of Port multiplexing and Remapping To input and output signals

Port multiplexing

Concept ：
One GPIO If it can be reused as a function pin of the built-in peripheral , So when this GPIO When used as a built-in peripheral , It's called reuse .

With USART1( A serial port 1) Take port multiplexing as an example .

This is a STM32F103ZET6《 Data manual 》 A partial screenshot of the pin information description table in .
You can see

• PA9 and PA10 The main functions of PA9 and PA10. That is, general input and output function .
• Among the selectable functions, the default reuse function is USART1_TX（ A serial port 1 Send pin ） and USART1_RX（ A serial port 1 Receive pin ）.

At this point we can say ,USART1_TX and USART1_RX Is reused in GPIO Of PA9 and PA10 Oral .

Configuration process of port multiplexing

After we know what class port reuse is, we need to configure it , How else can the chip know GPIO Is the port used as a general input and output port or a port multiplexing port ？

1. GPIO Clock enable

Port reuse is still used in the final analysis GPIO, Therefore, it is necessary to check the corresponding GPIO Carry out enabling . With USART1 For example , We know that it reuses GPIO yes PA Of the group IO mouth , So you need to GPIOA Carry out enabling .

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

In this meow's article STM32 Our clock system As mentioned in GPIO Is attached to APB2 Under the bus , So this function is used .

2. Multiplex peripheral clock enable

No matter what peripherals are used , Not only does it use GPIO, And the peripheral itself should also be used , Therefore, when using built-in peripherals, it is also necessary to enable . With USART1 For example

RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

USART1( A serial port 1) It is also attached to APB2 On the bus .

3. Port mode configuration

Will be GPIO and USAR1 Enable later , Next we need to tell CPU The IO The port uses the port multiplexing function .

stay STM32F103ZET6 Chip 《 Chinese Reference Manual 》 In the reuse function configuration table , Lists in detail when port multiplexing ,GPIO How to configure . That is to say GPIO The initialization .
With USART1_TX and USART1_RX For example ：

USART1_TX( The sender )

• In full duplex mode ,GPIO It needs to be configured into push-pull multiplexing output mode .

USART1_RX( The receiver )

• In full duplex mode ,GPIO It needs to be configured as floating input or pull-up input .

In the code

GPIO_TypeDef GPIO_InitStructyre;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; //PA.9// Multiplexing push pull output 
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; 
GPIO_Init(GPIOA, &GPIO_InitStructure);
  
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;//PA10 PA.10  Floating input 
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;// Floating input 
GPIO_Init(GPIOA, &GPIO_InitStructure);  

The above is based on USART1 For example , The whole process of port multiplexing configuration . After the above configuration ,PA9 and PA10 And it became USART1_TX and USART1_RX The pin of , It is no longer a general input and output port .

Port reimage

Port remapping is actually similar to port multiplexing , Port multiplexing is built-in peripherals, and the multiplexing port is fixed , It is necessary to find the multiplexing corresponding to different peripherals through the pin description in the data manual GPIO mouth .
The mapped port of port remapping is also fixed , It also needs to be found by looking up the table , The mapping port and multiplexing port are not the same .

Concept ：

• The pin of a peripheral has a default port , You can also set the remapping register , Map the pins of this peripheral to other ports .

Purpose ：

• In order to allow design engineers to better arrange the direction and function of pins , Potentially reduce the cross interference of signals .

This is a STM32F103ZET6 chip 《 Chinese Reference Manual 》 Re image configuration table in . With USART1 For example , The table shows ,USART1_TX and USART1_RX After remapping GPIO The mouth is PB6 and PB7.

It can also be done through 《 Data manual 》 See in the pin description table in ,PB6 and PB7 Among the selectable functions , After remapping, the corresponding is USART1_TX and USART1_RX.

Port remapping is also divided into incomplete remapping and complete remapping

Partial re image and full re image

With USART3 For example , stay 《 Chinese Reference Manual 》 In the re image configuration table of ,USART3 A common need 5 One pin , Namely USART3_TX,USART3_RX,USART3_CK,USART3_CTS,USART3_RTS.

When there is no re image

• This 5 Ports use the port multiplexing function by default , They correspond to PB10 To PB14.

When partially reimaging

• among USART3_TX,USART3_RX,USART3_CK These three ports are no longer port multiplexed PB10 To PB12, But the remake became PC10 To PC12, and USART3_CTS and USART3_RTS It still corresponds to port multiplexing PB13 and PB14.

Complete remapping

• USART3 Of 5 All ports are reimagined to the new port , Corresponding PD8 To PD12 Five ports .

in general , Partial remapping refers to the remapping of some pins of built-in peripherals , There are also some pins corresponding to the default port multiplexing . Full remapping means that all pins of built-in peripherals are remapped .

The configuration process of re image

After knowing what is re image , We are going to use it .

1. Enable remapped GPIO.

After remapping, the new GPIO, So it is necessary to enable , Only after enabling, should IO Eloquence will be opened . With USART3 For example ：
When partially reimaging ：

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);

After partial remapping, two groups are used IO mouth , So you need to GPIOC and GPIOB Are enabled
Complete remapping

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOD, ENABLE);

After completely remapping ,USART3 Of 5 All pins are remapped to GPIOD Of the group IO On the mouth , So just enable GPIOD that will do .

2. Enable built-in peripherals

RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);

In the article on clock system, Ben meow mentioned ,USART3 It's mounted on APB1 On the bus , So the function used is this .

3. Can make AFIO The clock

For registers AFIO_MAPR,AFIO_EXTICRX and AFIO_EVCR Before reading and writing , Should be opened first AFIO The clock .

• AFIO_MAPR： Configure reuse function remapping
  AFIO_EXTICRX: Configure external breakline mapping
  AFIO_EVCR: To configure EVENTOUT Event output

RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);

AFIO The function auxiliary register is generally mounted in APB2 On the bus , So use this function .

4. Turn on the re image

After enabling the required registers, we go to the last step , Configure reimage .
We started with GPIO Find the function to open the re image in the relevant functions GPIO_PinRemapConfig().

The first parameter of this function has many , As shown in the above figure , Pass the parameters representing the peripherals corresponding to the re image and the re image mode to the start re image function .

GPIO_PinRemapConfig(GPIO_PartialRemap_USART3,ENABLE);// Partial remapping 
GPIO_PinRemapConfig(GPIO_FullRemap_USART3,ENABLE);// Complete remapping 

The second parameter only ENABLE and DISABLE, That is, decide whether to enable the re image .

After the above 4 Step by step, you will succeed USART3 Some ports of are remapped to PC10 To PC12, Or all ports are remapped to PD8 To PD12 On .

summary

Whether it is port multiplexing or port re imaging , All for the purpose of using the built-in peripherals of the chip , Only through port multiplexing or re imaging GPIO To connect with built-in peripherals , Deliver information to peripherals . Generally, port multiplexing is enough for us .