Working with STM32 and UART part 2: Sending strings and variable polling mode

Posted August 19, 2021 by Husamuldeen in Embedded Systems, Peripheral Drivers, STM32

In previous guide(part 1), we looked for how to send a single character. Now we will extend the usage of uart module to send a string contains “Hello from stm32f4” and a variable as “my variable is variable”

In this guide we will cover the following:

Extra steps needed to send a string
Code
Results

1. Extra steps needed to send a string

Starting from part 1, we need to add the following two header file

#include "stdio.h" //stdio which allows us to use sprinttf 
#include "stdint.h" //standardd int defention

then the prototype of the function to send a string

void UART_Write_String(char *p);

then the buffer to hold the data and variable

char buffer[40]={'0'};
unsigned int variable;

Now for the function that allows us to print the string

void UART_Write_String(char *p)
	{
	while(*p!='\0')
{
USART_write(*p);
p++;
}
}

The function works as following

First, we pass the string as argument, then it sends the string character by character until reaches NULL (‘\0’) then it stops

2. Code

#include "stm32f4xx.h"                  // Device header
#include "stdio.h"
#include "stdint.h"
void USART_write(int ch);
void USART2_Init(void);
void delay(int delayms);
void UART_Write_String(char *p);

char buffer[40]={'0'};
unsigned int variable;

int main(){

USART2_Init();
while(1){
UART_Write_String("---------------------------\r\n");
UART_Write_String("hello from stm32f411RE\r\n");
sprintf(buffer,"my variable is %u \r\n",++variable);
UART_Write_String(buffer);
UART_Write_String("---------------------------\r\n");
//variable=variable+1;
delay(1000);
}
}

void USART2_Init(void){
RCC->APB1ENR|=RCC_APB1ENR_USART2EN;
RCC->AHB1ENR|=RCC_AHB1ENR_GPIOAEN;
GPIOA->AFR[0]=0x0700;
GPIOA->MODER|=(1<<5);//set bit5
GPIOA->MODER&=~(1<<4);//reset bit4
USART2->BRR  = 0x0681;    //9600 @16MHz
USART2->CR1  |=0x2008; // enable tx

}

void USART_write(int ch){
while(!(USART2->SR&0x0080)){
}
USART2->DR=(ch);
	
}

void UART_Write_String(char *p)
	{
	while(*p!='\0')
{
USART_write(*p);
p++;
}
}


void delay(int delayms){
volatile int i;
	for(; delayms>0;delayms--){
	for(i=0;i<3192;i++);
	}
}