STM32f3 embedded comparators

[arganasss]

Posted on January 16, 2014 at 16:09

Firstable, sorry for so many new topics, but as i dig deeper and deeper into programming stm32 boards, i find a lot new questions. I wasn't able to find a topic which relates to my problem, so i just created a new, and here is my question: I know stm32f3 board has embedded comparators. Is it possible to put a ramp signal from external generator into one into I/O pins and the same signal into one of comparator's input. Then detect a falling edge of the signal go to interrupt which starts timer, and stops it when signal reaches threshold value? Is it possible to change treshold value in my program? Maybe there are some examples written by ST for comparators usage? Any help and answers to my this problem will be highly appreciated. Thanks in advance.

Edit: I found example on OPAMP_PGA for stm32, but that just gives me understanding how to configure comparator.

[arganasss]

Posted on January 20, 2014 at 18:10

Edit: Thank you for your help. Now my code is working and comparator work's as it should. I have a question though. If i look up no PF4 with scope, i see small voltage “jumps“ even without running my code. I also see that on some PA pins. Have u any idea why is that?

Thank you very much for your help again and answers.

[raptorhal2]

Posted on January 20, 2014 at 20:43

i see small voltage “jumps“

PF4 pin is digital logic. As long as it doesn't jump between logic level ''0'' and ''1'' levels, this is normal noise pickup.

If you see the same problem on PA1 when the signal source is connected, then further investigation might be needed.

Cheers, Hal

[arganasss]

Posted on January 24, 2014 at 11:41

Thank you for your help. I still didn't manage to do what i want. I want to use the EXTI interrupt to detect the falling edge of the signal connected to the I/O pin, then start a timer which would stop when comparator output goes to high level, however nothing works. My code now goes as follows:

#include

''main.h''

#include

''stdio.h''

TIM_ICInitTypeDef TIM_ICInitStructure;

GPIO_InitTypeDef GPIO_InitStructure;

TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;

NVIC_InitTypeDef NVIC_InitStructure;

EXTI_InitTypeDef EXTI_InitStructure;

COMP_InitTypeDef COMP_InitStructure;

void

EXTI1_IRQHandler(

void

)

{

if

(EXTI_GetITStatus(EXTI_Line1) != RESET)

//

Check

if

EXTI_Line1

is

asserted

{

GPIOE->ODR ^= GPIO_Pin_8;

}

EXTI_ClearITPendingBit(EXTI_Line1);

//

Clear

EXTI

LINE1

pending

bit

}

void

EXTI1_Config(

void

)

{

SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOA, EXTI_PinSource1);

//

Connect

EXTI1

Line

to

PA1

pin

/*

Configure

EXTI1

line

*/

EXTI_InitStructure.EXTI_Line = EXTI_Line1;

//

Line1

EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;

//

Interrupt

mode

EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;

//

Detect

falling

edge

of

the

external

signal

connected

to

PA1

EXTI_InitStructure.EXTI_LineCmd = ENABLE;

//

Enable

EXTI

line

EXTI_Init(&EXTI_InitStructure);

//

Send

parameters

to

the

registers

/*

Configure

NVIC

*/

NVIC_InitStructure.NVIC_IRQChannel = EXTI1_IRQn;

//

Select

NVIC

channel

to

be

configured

NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority =

0x0F

;

//

Set

priority

to

the

lowest

NVIC_InitStructure.NVIC_IRQChannelSubPriority =

0x0F

;

//

Set

sub-priority

to

the

lowest

NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

//

Enable

IRQ

channel

NVIC_Init(&NVIC_InitStructure);

//

Send

parameters

to

the

registers

}

void

Comparator_Config(

void

)

{

/*

Configure

PA1

analog

mode:

It

is

used

as

Comparator1

analog

input

*/

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_1;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;

//

Analog

mode

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_Init(GPIOA, &GPIO_InitStructure);

/*

Configure

PF4

in

Alternate

Function

mode:

it

is

used

as

Comparator1

output

*/

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;

//

Alternate

function

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_Init(GPIOF, &GPIO_InitStructure);

GPIO_PinAFConfig(GPIOF, GPIO_PinSource4, GPIO_AF_2);

//

Connect

Port

A

pin

6

to

comparator

output

COMP_InitStructure.COMP_InvertingInput = COMP_InvertingInput_VREFINT;

COMP_InitStructure.COMP_NonInvertingInput = COMP_NonInvertingInput_IO1;

COMP_InitStructure.COMP_Output = COMP_Output_None;

COMP_InitStructure.COMP_BlankingSrce = COMP_BlankingSrce_None;

COMP_InitStructure.COMP_OutputPol = COMP_OutputPol_NonInverted;

COMP_InitStructure.COMP_Hysteresis = COMP_Hysteresis_No;

//

Do

not

use

Hysteresis

COMP_InitStructure.COMP_Mode = COMP_Mode_UltraLowPower;

//

Ultra

low

power

mode

COMP_Init(COMP_Selection_COMP1, &COMP_InitStructure);

//

Enable

COMP

parameters

COMP_Cmd(COMP_Selection_COMP1, ENABLE);

//

Enable

comparator1

}

int

main(

void

)

{

RCC->AHBENR |=

1

<<

21

;

//

Enable

clock

for

port

E

RCC->APB1ENR |=

1

<<

1

;

//

enable

clock

for

Timer3

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

//

Timer2

clock

on

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);

//

GPIOA

clock

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOF, ENABLE);

RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE);

//

Enable

the

SYSCFG

APB

clock

to

get

write

access

to

comparator

register

and

EXTI

line

interrupts

COMP_DeInit(COMP_Selection_COMP1);

//

Reset

comp1

parameteres

to

default

values

//

Port

E

pin

8

(blue

LED)

configuration

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_Init(GPIOE, &GPIO_InitStructure);

EXTI1_Config();

EXTI1_IRQHandler();

//

Comparator_Config();

//

Uncomment

this

line

and

comparator

works,

but

the

code

never

jumps

to

EXTI1_IRQHandler.

Comment

this

line

and

then

code

goes

to

EXTI1_IRQHandler

while

(

1

)

{

//

Do

nothing

}

}

As i stated in the code, uncommenting the line Comparator_Config() in the main function get's comparator to work, but then code never jumps to EXTI line IRQ handler. If i comment that line, comparator obviously doesn't work, but then my code is able to jump to EXTI_IRQHandler. Could anyone explain why this behaviour is caused? Is it because EXTI Line 1 uses the same pin as Comparator input? OR is it because that it requires GPIO pins to be configured in input mode if i want to use EXTI interrupt, but i already have configured the pin in analog mode for Comparator? Or i have completely wrong understanding of how EXTI interrupts work? I'll appreciate any help for solving this problem. Thanks in advance.

[raptorhal2]

Posted on January 24, 2014 at 22:21

You seem to have taken a step backwards. After setting up your comparator falling edge detect criteria and connecting the comparator output to PF4, you then connect the EXT interrupt to PA1, bypassing the comparator output.

My guess is that you are confused over the edge detector logic in the EXT ciruitry. As I stated before, this is a digital logic edge criteria, your sine wave input is an analog signal, so you need to use the setup you have in place for the comparator inputs as your edge detector.

See Section 11.2.6 in the F3 reference manual. The table there identifies EXTI4 as the interrupt connected to PF4, and that should then be the handler that starts the timer going.

After you get the timer going correctly, then you need to set up another comparator with low level detection connected to another EXT interrupt to stop the timer when the low level criteria is met.

Cheers, Hal

[arganasss]

Posted on January 24, 2014 at 23:32

From your post i now see that i misunderstood the EXTI interrupt and edge detecting criteria. Thanks a lot for your help and time. I'll try to do this now and give you a feedback. 

Cheers, Arganas.

[arganasss]

Posted on January 28, 2014 at 14:12

I just wanted to give you a feedback. Thank you for your help, time and comments. It helped me a lot and i managed to do what i want.