This paper mainly introduces the basic principle of STM32 serial communication and how to use assembly language to make MCU communicate with computer.
catalogue
1, Introduction to USARTUniversal synchronous asynchronous receiver and transmitter is a serial communication device, which can flexibly exchange full duplex data with external devices.
Serial communication generally transmits data in frame format, that is, frame by frame transmission. Each frame contains start signal, data information, stop information and possibly verification information. USART has specific provisions on these transmission parameters. Of course, there is not only one parameter value. Many parameter values can be customized to enhance its compatibility.
Function diagram
2, Assembly code
(1) Project creation
Create a new project
Because it's an assembly language, don't check it
Add assembly file
(2) Code implementation
The code is as follows
;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, #'o' bl send_a_char mov r0, #'r' bl send_a_char mov r0, #'l' bl send_a_char mov r0, #'d' bl send_a_char mov r0, #'\n' bl send_a_char b main ;Subroutine serial port 1 sends a character send_a_char push 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 bx lr ;subroutine led twinkle LedFlas push 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 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
Compile without error
The board I use is stm32f1103RC. Just connect a USB conversion cable
Open mcuisp for burning
Next, open the upper computer and serial communication assistant. I use SSCOM here
Select the CH340 communication port in the upper left corner
Click open serial port in the lower left corner
Hello received world, success
Serial communication allows us to communicate with computers. The simple output hello world is just entering the big door of serial communication, which is just a foundation. The code of this time refers to others. There are still many places that assembly language does not understand. There is still a long way to go, so we still have to learn.
5, Reference articlesCreating STM32 assembler based on MDK: serial port output Hello world_ssj925319 blog - CSDN blog