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jjhopkotcha
jjhopkotcha
Associate II
July 22, 2011
Question

Defining GPIO ports as inputs

  • July 22, 2011
  • 6 replies
  • 2879 views
Posted on July 22, 2011 at 11:07

Hi there, I am fairly new to programming these chips, I am currently coding using the IAR Embedded Workspace and loading my program onto an STM32F100 LQFP48 chip.

Currently I have pins PB8, PB9, PB10, PB11, PB12, PA11, PA12, PB15 set up as outputs which power 8 LED's. 

I am using to of the outputs to control a small DC motor using a H-Bridge. In order to control the movement of my DC motor I have a couple of micro-switches which limit the rotation of my motor. I need my program to be able to respond to signals from these micro-switches which requires defining some of my GPIO's on my chip as inputs. 

I have a small PCB board for programming my chip and there are lots of test pins which I could solder onto, many of these are GPIO's such as PB0-PB2, presumably these would be fine. 

Any help would be seriously appreciated. 

Thanks

#lqfp48 #gpio #stm32f100
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6 replies

infoinfo966
infoinfo966
Associate II
July 22, 2011
Posted on July 22, 2011 at 11:39

What exactly do you want to know?

Do you use the ST Standard Peripheral Libraries?

Best

Tom

jjhopkotcha
jjhopkotchaAuthor
Associate II
July 22, 2011
Posted on July 22, 2011 at 12:27

Yes as far as I am aware I do. There are so many functions containing GPIO such as GPIO_Remap or GPIO_typedef etc. 

I am wondering what sort of line of code would set up, say for example PB0 and PB1 as a logical input enabling my microprocessor to respond to my motor's position. 

Thanks

infoinfo966
infoinfo966
Associate II
July 22, 2011
Posted on July 22, 2011 at 13:19

That's pretty simple:

  GPIO_InitTypeDef GPIO_InitStructure;

  //IMportant, you always have to enable the Peripheral Clock before you can use a device

For you:

 

  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1 | GPIO_Pin_2;

  // now it depends if you want to use the internal PUSH UP/DOWN resistors, if so use

   //  GPIO_Mode_IPD = 0x28,

   // GPIO_Mode_IPU = 0x48,

  // if you have external pus ups/downs just

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;

      GPIO_Init(GPIOB, &GPIO_InitStructure);

 

Now you can poll the state of your PIN with

GPIO_ReadInputDataBit(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin);

I hope this helps

Best

Tom

jjhopkotcha
jjhopkotchaAuthor
Associate II
July 22, 2011
Posted on July 22, 2011 at 14:44

Thanks Tom, i'm definitely getting closer. Forgive me if i sound a little inexperienced with my questions. I believe in my code that GPIO_Pin_1 is being used to define PA0_WKUP and this is used as an interrupt to shut down my chip. 

I intend to use external pull down resistors so would this bit of code work for me,

GPIO_InitTypeDef GPIO_InitStructure;

  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE); // enable's the peripheral clock. 

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1 | GPIO_Pin_2;

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN; // this sets up input to be used with external push up/pull down resistors.

  GPIO_Init(GPIOB, &GPIO_InitStructure);

Thanks for your help thus far, I am struggling to realise where in this code i can know which pin of my chip is being defined and then when it comes to polling my input presumably i refer to the desired pin at this point (''__'') in the read data line and the x following GPIO would be B if im using PB1 or PB2...???

GPIO_ReadInputDataBit(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin ''__'' ); 

Thanks again, 

John

jjhopkotcha
jjhopkotchaAuthor
Associate II
July 22, 2011
Posted on July 22, 2011 at 18:36

Hi there,

I think i've cracked how to define any of my GPIO's as inputs or outputs, i am now struggling to poll a value for an input. 

i am using the following code to hopefully store a value or 1, or 0 into either of the variables M1_Status or M2_Status. 

int M1_Status (void)

{

  return (GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_0) ? 1:0);

}

int M2_Status (void)

{

  return (GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_1) ? 1:0);

}

Any help on how to extract a number from these inputs would be great. 

Thanks

John

infoinfo966
infoinfo966
Associate II
July 22, 2011
Posted on July 22, 2011 at 20:51

Hmmm...

M1_Status and M2_Status are not variables but functions as you defined them.

I have no idea what you want to achieve with your code, as GPIO_ReadInputDataBit

already returns an int with the result.

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