Скачать или смотреть Mastering Timer Input Capture Mode with STM32: Configuring for Accurate Timing with External Signals

Discover how to configure the STM32F446's timer to accurately capture input signals, ensuring precise timing for triggered events in your projects.
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Mastering Timer Input Capture Mode with STM32

When working on embedded systems, especially with microcontrollers like the STM32, there are times when you need precise timing capabilities. One common scenario involves triggering a timer with an external signal. If you've ever wondered how to achieve this, you're in the right place!

In this post, we will delve into a specific solution for using the TIM2 peripheral in the STM32F446 microcontroller, which allows you to count up to 90 microseconds at each rising edge of an external signal.

Understanding the Problem

The goal is clear: you want the timer to respond to an external signal that occurs every 1 millisecond, and you want it to count up to 90 microseconds with each rising edge of that signal. However, starting from scratch with timer configurations, especially in microcontrollers, can be complicated, particularly when using libraries that may not expose all the functionalities of the hardware.

Your initial configuration attempts using the HAL library and the Input Compare mode might not have achieved your desired results, leading to confusion on which callback mechanism to implement.

The Solution: Configuring the Timer Correctly

To effectively use the timer in response to an external trigger, follow these organized steps:

1. Switch to Trigger Mode

The first thing to understand is that Input Capture mode is not what you need here. Instead, you should use Trigger mode. This mode will allow the timer to start counting based on the external signal trigger rather than just capturing its current count.

Configuration Steps:

Set the field TIMx_CCMRx_CCxS to 0b11 (3) to configure the input as a trigger.

Set TIMx_SMCR_TS to select the channel intended for triggering.

Configure TIMx_SMCR_SMS to 0b110 (6) to start on the trigger signal.

2. Set Up Timer Parameters

Next, configure your timer settings to achieve the desired timing:

Prescaler: Ensure you set it properly to achieve the timing accuracy you need. You want the count duration to match 90 microseconds precisely.

Reload Register: Set it so the timer hits the desired count accurately. The timer should count up to 89 (with regards to a frequency of 50MHz).

One-Pulse Mode (OPM): Set TIMx_CR1_OPM to 1 to stop the counter from wrapping once it reaches the limit.

3. Trigger Output Configuration

Next up, configure the timer to output a trigger on update events:

Set TIMx_CR2_MMS to 0b010 so that your timer outputs a trigger on the update event.

4. Configure ADC Trigger

If you're using the ADC along with the timer, ensure that you set the ADCx_CR2_EXTSEL bits to 0b00110 for the TIM2 trigger output.

5. Using the Reference Manual

Though this might sound overwhelming, the STM32 reference manual is an invaluable resource. It thoroughly explains each register's fields, allowing you to verify your configuration step by step.

6. Avoid Mixing Libraries

It's crucial to avoid mixing the HAL library with direct register access; doing so may result in unforeseen issues or conflicts in your code.

Conclusion

Configuring timer input capture mode in STM32 for external triggers requires a thoughtful approach. By understanding the distinction between Input Capture and Trigger modes, and meticulously setting your timer's parameters, you can achieve precise timing suitable for various applications.

For more detailed guidance, don't hesitate to refer to the STM32 reference manual, which is your best friend in mastering these configurations.

If you're experiencing challenges or have questions, don’t hesitate to reach out or leave a comment below!