STM32CubeMX completes USART serial communication
catalogue
1, Serial port protocol
2, STM32CubeMX installation
3, USART serial communication program of STM32
4, Observe the waveform
5, Summary
1, Serial port protocol
1. USART introduction
In embedded development, UART serial communication protocol is one of our commonly used communication protocols (UART, I2C, SPI, etc.). Its full name is Universal Asynchronous Receiver/Transmitter. It is a kind of asynchronous serial communication protocol. Its working principle is to transmit each character of transmitted data bit by bit, It can convert the data to be transmitted between serial communication and parallel communication, and can flexibly exchange full duplex data with external devices.
2. Functional block diagram
3. UART communication protocol
1) Start bit
When no data is sent, the data line is in the logic "1" state; First, a logical "0" signal is sent to indicate the start of character transmission.
2) Data bit
Immediately after the start bit. The number of data bits can be 4, 5, 6, 7, 8, etc., forming a character. ASCII code is usually used. The transmission starts from the lowest bit and is positioned by the clock.
3) Parity bit
After adding this bit to the data, the number of bits of "1" should be even (even check) or odd (odd check), so as to verify the correctness of data transmission.
4) Stop bit
It is the end flag of a character data. It can be 1-bit, 1.5-bit and 2-bit high level. Because the data is timed on the transmission line and each device has its own clock, there may be a small synchronization between the two devices in the communication. Therefore, the stop bit not only indicates the end of transmission, but also provides an opportunity for the computer to correct clock synchronization. The more bits applicable to stop bits, the greater the tolerance of different clock synchronization, but the slower the data transmission rate.
5) Free bit or start bit
In the logic "1" state, it means that there is no data transmission on the current line and it enters the idle state.
In the logical "0" state, it indicates that the transmission of the next data segment begins.
6) Baud rate
It represents the number of symbols transmitted per second. It is an index to measure the data transmission rate. It is expressed by the number of carrier modulation state changes per unit time.
The commonly used baud rates are 9600, 115200
Time interval calculation: the time obtained by dividing 1 second by baud rate. For example, the time interval with baud rate of 9600 is 1s / 9600 (baud rate) = 104us.
4,
1) Serial Interface is abbreviated as serial port, also known as serial communication interface or serial communication interface (usually COM interface), which is an extended interface using serial communication mode. Serial Interface refers to the sequential transmission of data bit by bit. Its characteristic is that the communication line is simple. As long as a pair of transmission lines can realize two-way communication (the telephone line can be directly used as the transmission line), which greatly reduces the cost. It is especially suitable for long-distance communication, but the transmission speed is slow. Generally, it is the 9-pin trapezoidal interface behind the computer, which usually adopts RS232 signal.
2) RS-232: also known as standard serial port, the most commonly used serial communication interface. The traditional RS-232-C interface standard has 22 wires and adopts a standard 25 core D-type plug socket (DB25), which is later simplified to a 9-core D-type socket (DB9). RS-232 adopts unbalanced transmission mode, that is, the so-called single terminal communication. Because the difference between the transmission level and the reception level is only about 2V to 3V, its common mode suppression ability is poor. Coupled with the distributed capacitance on the twisted pair, the maximum transmission distance is about 15m and the maximum rate is 20kb/s. RS-232 is designed for point-to-point (i.e. only one pair of receiving and transmitting equipment) communication, and its driver load is 3 ~ 7k Ω. Therefore, RS-232 is suitable for communication between local devices.
3) TTL level: TTL level signal specifies that + 5V is equivalent to logic "1" and 0V is equivalent to logic "0" (when binary is used to represent data). Such data communication and level specification mode is called TTL (transistor transistor logic level) signal system. This is the standard technology of communication between various parts of equipment controlled by computer processor
4) USB to TTL: USB interface and TTL serial port cannot communicate directly, because the interface does not match and the level does not match. It is necessary to use peripheral devices to realize the conversion between interface and level. The conventional operation is to use chips such as CH340 and CP2102.
2, Installation and use of STM32CubeMX
(1) Stm32subemx installation
1. Installing the jdk environment
Download address: https://www.oracle.com/java/technologies/javase-downloads.html
2. Installing STM32CubeMX
Download address: https://www.st.com/en/development-tools/stm32cubemx.html
(1) Run the installer as an administrator and click next
(2) Check the accept... Option and click next
(3) Select the installation path. You can choose the default installation path or choose your own. The path cannot have Chinese. Click next
(4) Click OK on the pop-up page and then click next
(5) Click next after installation
Finally, click done to complete the installation
- Installation of solid silo
Run CubeMX and select the manage option under Help
Select the download version and click install now
(2) Use STM32CubeMX to generate relevant codes
1. Click new project to select the chip
2. Click SYS and select Serial Wire in the debug option
3. High speed clock crystal / ceramic resonator after clicking RCC
4. Click clock consultation pllclk
5. Set the corresponding pin to GPIO_OUT mode
6. Set the project name, path, and Toolchain/IDE, and then click GENERATE CODE in the upper right corner
7. Add code
Open the set project directory and open the MDK-ARM file. Open the project in keil and click main.c
Locate the while loop of the main function and insert the code
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_1,GPIO_PIN_RESET);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_3,GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_5,GPIO_PIN_SET);
HAL_Delay(1000);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_1,GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_3,GPIO_PIN_RESET);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_5,GPIO_PIN_SET);
HAL_Delay(1000);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_1,GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_3,GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOA,GPIO_PIN_5,GPIO_PIN_RESET);
HAL_Delay(1000);
Click the magic wand, check Create Hex File in the output interface, and the Debug interface is set as follows
compile
Open mcuisp, select LED.hex file, set relevant parameters as follows, and burn
LED light effect
STMCubemx implementation of LED lamp
3, USART serial communication
(1) Implementation of HAL Library
1. Create a new project
- File – new project – select STM32F103C8 chip and Start Project in the upper right corner
- Configure the clock. Select RCC – crystal / ceramic resonator
- Select USART2 – Mode – Asynchronous
- Clock Configuration – set PLLCLK, HSE and PLLMul
- Interrupt settings, USART2 – NVIC Settings – NVIC Interrupt Table
- Set the project name and path, and modify other settings as follows:
- Click Code Generator, check relevant items, and click GENERATE CODE
2 insert the code. Open the set project directory, enter the MDK ARM file, and open the keil file Hello
- Open the main.c file, locate the while loop of the main function, and insert the following code
char data[]="hello windows!\n";//Data sent HAL_UART_Transmit(&huart2, (uint8_t *)data, 15, 0xffff);//send out HAL_Delay(1000);//delayed
- Click the magic wand to open the Output and Debug interfaces respectively. The settings are as follows
- Serial port download
Pin connection:
3.3v-3
GND-G
TXD-PA10
RXD-PA9
BOOT0 is set to 1 and BOOT1 is set to 0.
Open mcuisp and select the Hello.hex file to burn
(2) Register GPIO port mode implementation
-
Open kei and select project → new vision project to create a new project (this time, it is not necessary to check CORE and Start up)
-
Insert code after selecting Add asm file
;RCC Register address mapping
RCC_BASE EQU 0x40021000
RCC_CR EQU (RCC_BASE + 0x00)
RCC_CFGR EQU (RCC_BASE + 0x04)
RCC_CIR EQU (RCC_BASE + 0x08)
RCC_APB2RSTR EQU (RCC_BASE + 0x0C)
RCC_APB1RSTR EQU (RCC_BASE + 0x10)
RCC_AHBENR EQU (RCC_BASE + 0x14)
RCC_APB2ENR EQU (RCC_BASE + 0x18)
RCC_APB1ENR EQU (RCC_BASE + 0x1C)
RCC_BDCR EQU (RCC_BASE + 0x20)
RCC_CSR EQU (RCC_BASE + 0x24)
;AFIO Register address mapping
AFIO_BASE EQU 0x40010000
AFIO_EVCR EQU (AFIO_BASE + 0x00)
AFIO_MAPR EQU (AFIO_BASE + 0x04)
AFIO_EXTICR1 EQU (AFIO_BASE + 0x08)
AFIO_EXTICR2 EQU (AFIO_BASE + 0x0C)
AFIO_EXTICR3 EQU (AFIO_BASE + 0x10)
AFIO_EXTICR4 EQU (AFIO_BASE + 0x14)
;GPIOA Register address mapping
GPIOA_BASE EQU 0x40010800
GPIOA_CRL EQU (GPIOA_BASE + 0x00)
GPIOA_CRH EQU (GPIOA_BASE + 0x04)
GPIOA_IDR EQU (GPIOA_BASE + 0x08)
GPIOA_ODR EQU (GPIOA_BASE + 0x0C)
GPIOA_BSRR EQU (GPIOA_BASE + 0x10)
GPIOA_BRR EQU (GPIOA_BASE + 0x14)
GPIOA_LCKR EQU (GPIOA_BASE + 0x18)
;GPIO C Mouth control
GPIOC_BASE EQU 0x40011000
GPIOC_CRL EQU (GPIOC_BASE + 0x00)
GPIOC_CRH EQU (GPIOC_BASE + 0x04)
GPIOC_IDR EQU (GPIOC_BASE + 0x08)
GPIOC_ODR EQU (GPIOC_BASE + 0x0C)
GPIOC_BSRR EQU (GPIOC_BASE + 0x10)
GPIOC_BRR EQU (GPIOC_BASE + 0x14)
GPIOC_LCKR EQU (GPIOC_BASE + 0x18)
;Serial port 1 control
USART1_BASE EQU 0x40013800
USART1_SR EQU (USART1_BASE + 0x00)
USART1_DR EQU (USART1_BASE + 0x04)
USART1_BRR EQU (USART1_BASE + 0x08)
USART1_CR1 EQU (USART1_BASE + 0x0c)
USART1_CR2 EQU (USART1_BASE + 0x10)
USART1_CR3 EQU (USART1_BASE + 0x14)
USART1_GTPR EQU (USART1_BASE + 0x18)
;NVIC Register address
NVIC_BASE EQU 0xE000E000
NVIC_SETEN EQU (NVIC_BASE + 0x0010)
;SETENA Starting address of register array
NVIC_IRQPRI EQU (NVIC_BASE + 0x0400)
;Start address of interrupt priority register array
NVIC_VECTTBL EQU (NVIC_BASE + 0x0D08)
;Address of vector table offset register
NVIC_AIRCR EQU (NVIC_BASE + 0x0D0C)
;Address of application interrupt and reset control register
SETENA0 EQU 0xE000E100
SETENA1 EQU 0xE000E104
;SysTick Register address
SysTick_BASE EQU 0xE000E010
SYSTICKCSR EQU (SysTick_BASE + 0x00)
SYSTICKRVR EQU (SysTick_BASE + 0x04)
;FLASH Buffer register address image
FLASH_ACR EQU 0x40022000
;SCB_BASE EQU (SCS_BASE + 0x0D00)
MSP_TOP EQU 0x20005000
;Starting value of main stack
PSP_TOP EQU 0x20004E00
;Process stack start value
BitAlias_BASE EQU 0x22000000
;Bit alias area start address
Flag1 EQU 0x20000200
b_flas EQU (BitAlias_BASE + (0x200*32) + (0*4))
;Bit address
b_05s EQU (BitAlias_BASE + (0x200*32) + (1*4))
;Bit address
DlyI EQU 0x20000204
DlyJ EQU 0x20000208
DlyK EQU 0x2000020C
SysTim EQU 0x20000210
;Constant definition
Bit0 EQU 0x00000001
Bit1 EQU 0x00000002
Bit2 EQU 0x00000004
Bit3 EQU 0x00000008
Bit4 EQU 0x00000010
Bit5 EQU 0x00000020
Bit6 EQU 0x00000040
Bit7 EQU 0x00000080
Bit8 EQU 0x00000100
Bit9 EQU 0x00000200
Bit10 EQU 0x00000400
Bit11 EQU 0x00000800
Bit12 EQU 0x00001000
Bit13 EQU 0x00002000
Bit14 EQU 0x00004000
Bit15 EQU 0x00008000
Bit16 EQU 0x00010000
Bit17 EQU 0x00020000
Bit18 EQU 0x00040000
Bit19 EQU 0x00080000
Bit20 EQU 0x00100000
Bit21 EQU 0x00200000
Bit22 EQU 0x00400000
Bit23 EQU 0x00800000
Bit24 EQU 0x01000000
Bit25 EQU 0x02000000
Bit26 EQU 0x04000000
Bit27 EQU 0x08000000
Bit28 EQU 0x10000000
Bit29 EQU 0x20000000
Bit30 EQU 0x40000000
Bit31 EQU 0x80000000
;Vector table
AREA RESET, DATA, READONLY
DCD MSP_TOP ;Initialize main stack
DCD Start ;Reset vector
DCD NMI_Handler ;NMI Handler
DCD HardFault_Handler ;Hard Fault Handler
DCD 0
DCD 0
DCD 0
DCD 0
DCD 0
DCD 0
DCD 0
DCD 0
DCD 0
DCD 0
DCD 0
DCD SysTick_Handler ;SysTick Handler
SPACE 20 ;Reserved space 20 bytes
;Code snippet
AREA |.text|, CODE, READONLY
;Main program start
ENTRY
;Instructs the program to execute from here
Start
;Clock system settings
ldr r0, =RCC_CR
ldr r1, [r0]
orr r1, #Bit16
str r1, [r0]
;Enable external crystal oscillator
;Start external 8 M Crystal oscillator
ClkOk
ldr r1, [r0]
ands r1, #Bit17
beq ClkOk
;Wait for the external crystal oscillator to be ready
ldr r1,[r0]
orr r1,#Bit17
str r1,[r0]
;FLASH Buffer
ldr r0, =FLASH_ACR
mov r1, #0x00000032
str r1, [r0]
;set up PLL The PLL magnification is 7,HSE Input no frequency division
ldr r0, =RCC_CFGR
ldr r1, [r0]
orr r1, #(Bit18 :OR: Bit19 :OR: Bit20 :OR: Bit16 :OR: Bit14)
orr r1, #Bit10
str r1, [r0]
;start-up PLL Phase locked loop
ldr r0, =RCC_CR
ldr r1, [r0]
orr r1, #Bit24
str r1, [r0]
PllOk
ldr r1, [r0]
ands r1, #Bit25
beq PllOk
;choice PLL Clock as system clock
ldr r0, =RCC_CFGR
ldr r1, [r0]
orr r1, #(Bit18 :OR: Bit19 :OR: Bit20 :OR: Bit16 :OR: Bit14)
orr r1, #Bit10
orr r1, #Bit1
str r1, [r0]
;other RCC Related settings
ldr r0, =RCC_APB2ENR
mov r1, #(Bit14 :OR: Bit4 :OR: Bit2)
str r1, [r0]
;IO port settings
ldr r0, =GPIOC_CRL
ldr r1, [r0]
orr r1, #(Bit28 :OR: Bit29)
;PC.7 Output mode,Maximum speed 50 MHz
and r1, #(~Bit30 & ~Bit31)
;PC.7 Universal push-pull output mode
str r1, [r0]
;PA9 Serial port 0 transmitting pin
ldr r0, =GPIOA_CRH
ldr r1, [r0]
orr r1, #(Bit4 :OR: Bit5)
;PA.9 Output mode,Maximum speed 50 MHz
orr r1, #Bit7
and r1, #~Bit6
;10: Multiplexing function push-pull output mode
str r1, [r0]
ldr r0, =USART1_BRR
mov r1, #0x271
str r1, [r0]
;Configure baud rate-> 115200
ldr r0, =USART1_CR1
mov r1, #0x200c
str r1, [r0]
;USART Module total enable send and receive enable
;71 02 00 00 2c 20 00 00
;AFIO Parameter setting
;Systick Parameter setting
ldr r0, =SYSTICKRVR
;Systick Initial installation value
mov r1, #9000
str r1, [r0]
ldr r0, =SYSTICKCSR
;set up,start-up Systick
mov r1, #0x03
str r1, [r0]
;NVIC
;ldr r0, =SETENA0
;mov r1, 0x00800000
;str r1, [r0]
;ldr r0, =SETENA1
;mov r1, #0x00000100
;str r1, [r0]
;Switch to user level line program mode
ldr r0, =PSP_TOP
;Initialize thread stack
msr psp, r0
mov r0, #3
msr control, r0
;initialization SRAM register
mov r1, #0
ldr r0, =Flag1
str r1, [r0]
ldr r0, =DlyI
str r1, [r0]
ldr r0, =DlyJ
str r1, [r0]
ldr r0, =DlyK
str r1, [r0]
ldr r0, =SysTim
str r1, [r0]
;Main cycle
main
ldr r0, =Flag1
ldr r1, [r0]
tst r1, #Bit1
;SysTick Generate 0.5s,Set bit 1
beq main ;0.5s The flag is not set yet
;0.5s The flag has been set
ldr r0, =b_05s
;Bit band operation reset 0.5s sign
mov r1, #0
str r1, [r0]
bl LedFlas
mov r0, #'h'
bl send_a_char
mov r0, #'e'
bl send_a_char
mov r0, #'l'
bl send_a_char
mov r0, #'l'
bl send_a_char
mov r0, #'o'
bl send_a_char
mov r0, #' '
bl send_a_char
mov r0, #'w'
bl send_a_char
mov r0, #'i'
bl send_a_char
mov r0, #'n'
bl send_a_char
mov r0, #'d'
bl send_a_char
mov r0, #'o'
bl send_a_char
mov r0, #'w'
bl send_a_char
mov r0, #'s'
bl send_a_char
mov r0, #'\n'
bl send_a_char
b main
;Subroutine serial port 1 sends a character
send_a_char
push {r0 - r3}
ldr r2, =USART1_DR
str r0, [r2]
b1
ldr r2, =USART1_SR
ldr r2, [r2]
tst r2, #0x40
beq b1
;Send complete(Transmission complete)wait for
pop {r0 - r3}
bx lr
;subroutine led twinkle
LedFlas
push {r0 - r3}
ldr r0, =Flag1
ldr r1, [r0]
tst r1, #Bit0
;bit0 Flashing flag bit
beq ONLED ;Open for 0 led lamp
;Off for 1 led lamp
ldr r0, =b_flas
mov r1, #0
str r1, [r0]
;The flashing flag position is 0,The next status is on
;PC.7 Output 0
ldr r0, =GPIOC_BRR
ldr r1, [r0]
orr r1, #Bit7
str r1, [r0]
b LedEx
ONLED
;Open for 0 led lamp
ldr r0, =b_flas
mov r1, #1
str r1, [r0]
;The flashing flag position is 1,The next status is off
;PC.7 Output 1
ldr r0, =GPIOC_BSRR
ldr r1, [r0]
orr r1, #Bit7
str r1, [r0]
LedEx
pop {r0 - r3}
bx lr
;Abnormal program
NMI_Handler
bx lr
HardFault_Handler
bx lr
SysTick_Handler
ldr r0, =SysTim
ldr r1, [r0]
add r1, #1
str r1, [r0]
cmp r1, #500
bcc TickExit
mov r1, #0
str r1, [r0]
ldr r0, =b_05s
;The clock tick counter is set to 0 when it is greater than or equal to 500 times of clearing.5s Flag bit
;Bit band operation set 1
mov r1, #1
str r1, [r0]
TickExit
bx lr
ALIGN
;By using zero or null instructions NOP fill,Aligns the current position with a specified boundary
END
Click the magic wand, and the Output and Debug settings are the same as before.
Download the serial port, connect the corresponding pin and port, and open mcuisp burning
Serial port debugging
4, Observe the waveform
(1) Water lamp waveform
1. Register mode
See the blog for details
Waveform analysis diagram
2. HAL library mode
Turn on the logic analyzer
Add a pin and set the display type to bit
Click Run(F5) in the upper left corner,
(2) Serial port protocol
(1) Register mode
Compile and debug the program, open UART#1 and logic analyzer in serial windows in the menu bar, add USART1_SR, and set the Display Type to Bit.
The waveform diagram is as follows:
(2) HAL library mode
Open UART#1 and logic analyzer in serial windows in the menu bar, add usart2#u Sr, and set the Display Type to Bit.
The waveform diagram is as follows:
5, Summary
Thanks for helping students in the project process and providing information for a few unknown bloggers. Actually, this is supposed to be a relatively easy experiment to implement, but the software is too suck for the experiment task to be half done. The rest of the process is spent on restoring the normal use of keil5, because keil5 is unable to compile the program or to debug it in the process. Unable to output such and such errors as hello windows, but the solution of multi-party query on the Internet can not be changed as desired. It was delayed to complete the task of this experimental project as desired. It seems that their independent solution ability needs to be improved.