STM32F4 Discovery project with CMSIS library;
Modular Coding
In this example we will use from Example-1 as a template, and explian another project in Keil uVision.
We want to build a PWM in PD12 with "frequency = 1 kHz". We want to build PWM signal by set-and-resetting of a PD12 (not with using pin-out of a timer as you see in the datasheet of our micro-controller: TIM4-CH1).
We want to change duty cycle of signal by pressing user button in STM32F4-Discovery Board. Because user button in STM32F4-Discovery Board is connected to PA0 we need to set PA0 as input and because (as you can see in the User Manual of STM32F4-Discovery Board) PA0 is physically pull-down we need not to pull-down (or pull-up) PA0, but if we need to use a input pin as a input key we must pull-down (or pull-up) the pin for good performance of the the key. (designer and programmer maybe prefer pull-up or pull-down for a special application difference between to this and no-pull is when the pin is not connected to a voltage).
As you see in the above picture in STM32F4-Discovery Board PD12 is connected to Green-LED and with this exercise we can change the lightness of this LED.
1. Copy & past "LastName-StudentID-001", and rename it to "LastName-StudentID-002". Then Open "GPIO.uvprojx" using Keil uVision5.
2. Open "main.c" and change it to:
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#include "stm32f4xx.h"
void Key_Init(void);
void LED_Init(void);
void usDelay(unsigned long msTime);
void Set_Reset_LED1(unsigned long Delay);
int main(void){
unsigned long Delay=500;
char flag=0;
LED_Init();
Key_Init();
// Wait until PushButton is pressed PA0=1
while(!GPIO_ReadInputDataBit(GPIOA,GPIO_Pin_0));
while(1){
Set_Reset_LED1(Delay%1000);
if(Delay==1000) flag=1;
if(Delay==0 ) flag=0;
if(GPIO_ReadInputDataBit(GPIOA,GPIO_Pin_0)){
if(flag==0) Delay++;
if(flag==1) Delay--;
}
}
}
//--------------------------------------------------------------------
void Key_Init(void){
GPIO_InitTypeDef GPIO_InitStructure;
/* GPIOA Periph clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
/* Configure PA0 in input mode */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
GPIO_Init(GPIOA, &GPIO_InitStructure);
}
//--------------------------------------------------------------------
void LED_Init(void){
GPIO_InitTypeDef GPIO_InitStructure;
/* GPIOD Periph clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
/* Configure PD12 in output pushpull mode */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_Init(GPIOD, &GPIO_InitStructure);
}
//--------------------------------------------------------------------
void Set_Reset_LED1(unsigned long Delay){
GPIO_SetBits(GPIOD, GPIO_Pin_12);
usDelay(Delay);
GPIO_ResetBits(GPIOD, GPIO_Pin_12);
usDelay(1000-Delay);
}
//--------------------------------------------------------------------
void usDelay(unsigned long usTime){
unsigned long i,j, nCount=0x29;
for(i=0;i<usTime;i++)
for(j=0;j<nCount;j++);
}
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3. Press F7 (or click on 
) to compile and make sure your code do not has any error. Then click on 
to download code to flash memory.
THE END.
