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Zheng Liang
Zheng Liang
Associate III
March 2, 2018
Question

How to configure the starting direction of center-aligned Timer

  • March 2, 2018
  • 1 reply
  • 1839 views
Posted on March 02, 2018 at 06:25

Device: STM32F103

I wanna set the direction(counting up or down) when starting a center-aligned Timer, but once I set the DIR and then set the CMS to center-aligned mode, the DIR bit will be cleared by hardware.

I found this description in datasheet:

When starting in center-aligned mode, the current up-down configuration is used. It

means that the counter counts up or down depending on the value written in the DIR bit

in the TIMx_CR1 register. Moreover, the DIR and CMS bits must not be changed at the

same time by the software.

How could I start the center-aligned mode with down direction?

If someone knows, please tell me.

thanks.

#stm32
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    1 reply

    Jan Waclawek
    Jan Waclawek
    Visitor II
    March 2, 2018
    Posted on March 02, 2018 at 10:41

    Show us code.

    Read out the timer registers immediately before enabling it and check/post.

    What's the CNT startng position?

    JW

    Zheng Liang
    Zheng LiangAuthor
    Associate III
    March 3, 2018
    Posted on March 03, 2018 at 09:00

    Hi Jan, here are the codes：

    --------------------------------------------------------------------

    //Enbale Timer1 clock

    RCC->APB2ENR |= RCC_APB2ENR_TIM1EN;

    //Set single pulse mode

    TIM1->CR1 |= TIM_CR1_OPM;

    //Set Center-aligned mode 3

    TIM1->CR1 |= TIM_CR1_CMS;

    //Set prescaler

    TIM1->PSC = 0;

    //Set auto-reaload value

    TIM1->ARR = 71 * 4;

    //Set repetition

    TIM1->RCR = 2;

    //Channel 1 at Toggle Mode

    TIM1->CCMR1 |= 3 << 4;

    TIM1->CCR1 = TIM1->ARR >> 1;

    //Enable channel 1 output

    TIM1->CCER |= TIM_CCER_CC1E;

    TIM1->BDTR |= TIM_BDTR_MOE;

    //Set direction to downcounting

    TIM1->CR1 |= TIM_CR1_DIR;

    //Set counter register to max value

    TIM1->CNT = TIM1->ARR;

    //Enable Timer1

    TIM1->EGR |= TIM_EGR_UG;

    TIM1->CR1 |= TIM_CR1_CEN;

    --------------------------------------------------------------------

    The problem is when  Center-aligned mode 3 is set, the code to set direction bit in CR1 register to downcounting will not work at all.

    Is the Center-aligned mode direction could only be set by hardware? means the counter could only start with upcounting mode from the first time?

    Thanks,

    Zheng

    waclawek.jan
    waclawek.jan
    Super User
    March 4, 2018
    Posted on March 04, 2018 at 02:32

    Zheng,

    Your problem is in that you set up the bits in CR1 separately. Then, when you get to set DIR, the following note below DIR's description in RM applies:

    Note: This bit is read only when the timer is configured in Center-aligned mode or Encoder

    mode.

    Set CR1 at once, as the last line:

    TIM1->CR1 = TIM_CR1_DIR | TIM_CR1_OPM | TIM_CR1_CMS | TIM_CR1_CEN;

    Note also that setting TiMx_EGR.UG has quite an aggressive effect: it resets TIMx_CNT to 0, and clears the DIR bit.

    JW

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