STM32 Timer Calculator

This calculator will help you compute the required PSC and ARR values to achieve your desired timer interrupt period. Just put in the timer interrupt period, the clock frequency, and the ARR register width.

STM32 Timer Overview

STM32 microcontrollers have several general-purpose timers, advanced timers, and basic timers. The system clock drives each timer and can be configured to operate in various modes:

1. Time Base Generation: Used for delays or periodic interrupts.
2. PWM Mode: Generates pulse-width modulation signals.
3. Input Capture: Measures input signal characteristics like frequency or duty cycle.
4. Output Compare: Produces specific events at predefined times.

Timers have several parameters that determine their behavior:

• Prescaler (PSC): Divides the input clock frequency to slow down the timer.
• Auto-Reload Register (ARR): Defines the maximum count value for the timer.
• Counter (CNT): Holds the current count value and increments or decrements based on the configuration.

Calculating Timer Interrupt Values

The timer interrupt frequency depends on the system clock frequency, the prescaler, and the auto-reload value. Here’s how to calculate these values:

Formula

The timer frequency is given by:

$$f_{\text{timer}} = \frac{f_{\text{clk}}}{(\text{PSC} + 1)}$$

The timer interrupt period is then:

$$T_{\text{interrupt}} = (\text{ARR} + 1) \times \frac{1}{f_{\text{timer}}}$$

Where:

• 
  $f_{\text{clk}}$ 

  ​: System clock frequency.

• 
  $\text{PSC}$ 

  : Prescaler value.

• 
  $\text{ARR}$ 

  : Auto-reload register value.

Steps to Configure a Timer Interrupt

1. Determine Desired Interrupt Period: Define how frequently the interrupt should occur (e.g., every 1 ms).
2. Choose Prescaler: Calculate PSC to scale down the clock to a manageable frequency
   $$\text{PSC} = \frac{f_{\text{clk}}}{f_{\text{timer}}} – 1$$
3. Set Auto-Reload Value: Calculate ARR to achieve the desired period.
   $$\text{ARR} = \frac{T_{\text{interrupt}} \times f_{\text{timer}}}{1} – 1$$
4. Program Timer Registers: Load the PSC and ARR values into the timer registers.

STM32 timers are powerful tools for embedded applications, providing precise time control and event management. By understanding the relationship between the system clock, prescaler, and auto-reload values, developers can configure timers to generate interrupts at specific intervals, enabling efficient task scheduling and timing operations.