The STM32 microcontroller family offers a rich set of timer functionalities, making it highly versatile for various timing and control applications. Among its key features are advanced timers like TIM1 and TIM8, general-purpose timers such as TIM2 to TIM5, and basic timers like TIM6 and TIM7. Additionally, there are watchdog timers and the system timebase timer known as SysTick.
Basic timers, such as TIM6 and TIM7, provide only fundamental timing capabilities. They include a 16-bit auto-reload counter driven by a programmable prescaler, making them suitable for simple timing tasks.
General-purpose timers, including TIM2 to TIM5, offer more advanced functions beyond basic timing. These timers can capture input signal pulses (input capture), generate output waveforms (output compare and PWM), and support multiple operating modes. Each general-purpose timer operates independently without sharing resources with others, offering flexibility in design.
Advanced timers like TIM1 and TIM8 go even further. They not only include all the features of the basic and general-purpose timers but also support complex motor control functions. For example, they can generate six complementary signals with dead-time insertion, include a brake function, and manage advanced PWM configurations.
There are two types of watchdog timers: the independent watchdog (IWDG) and the window watchdog (WWDG). These are used for system monitoring and ensuring reliable operation by resetting the microcontroller if it becomes unresponsive.
The system timebase timer, SysTick, is a 24-bit downcounter that automatically reloads. It is commonly used for generating delays at the millisecond or microsecond level, providing a foundation for real-time operations.
### Introduction to STM32 General-Purpose Timer
The STM32 general-purpose timer is a 16-bit auto-reload counter (TIMx_CNT) driven by a programmable prescaler (TIMx_PSC). This timer is capable of measuring the pulse length of an input signal (input capture) or generating output waveforms (output compare and PWM). Each general-purpose timer is fully independent and does not share any internal resources with other timers.
Key features of the STM32 general-purpose timer (TIM2–TIM5) include:
- **16-bit up, down, or up/down auto-reload counter (TIMx_CNT)**
- **16-bit programmable prescaler (TIMx_PSC)** that can divide the clock frequency by any value from 1 to 65535
- **Four independent channels (TIMx_CH1–4)** that can be configured for:
- Input capture
- Output comparison
- PWM generation (edge-aligned or center-aligned mode)
- Single-pulse mode output
- **External signal input (TIMx_ETR)** for synchronization and timer interconnection (e.g., one timer controlling another)
- **Interrupt/DMA triggers** for events such as:
- Update (counter overflow/underflow, initialization)
- Trigger events (start, stop, initialize)
- Input capture and output compare
- Quadrature encoder and Hall sensor support
- External clock input or cycle current management
### STM32 General-Purpose Timer Registers
1. **Auto-reload register (TIMx_ARR)**
This register has two physical parts: one that can be directly accessed by the programmer and another, called the shadow register, which is not visible. The shadow register is what actually controls the timer’s behavior. The APRE bit in the TIMx_CR1 register determines when the preload value is transferred to the shadow register—either immediately (APRE=0) or on each update event (APRE=1).
2. **Prescaler register (TIMx_PSC)**
This register divides the input clock frequency before it is supplied to the counter. There are four possible clock sources for the timer:
- Internal clock (CK_INT)
- External clock mode 1 (TIx)
- External clock mode 2 (ETR)
- Internal trigger (ITRx)
The clock source is selected using bits in the TIMx_SMCR register. The general-purpose timer's clock is derived from APB1, and when APB1 is not divided, the timer clock is equal to the APB1 clock. Advanced timers, however, use APB2 as their clock source.
3. **Counter register (TIMx_CNT)**
This register holds the current count value of the timer.
4. **Status register (TIMx_SR)**
This register indicates whether certain events or interrupts have occurred.
5. **DMA/Interrupt Enable Register (TIMx_DIER)**
This register controls which interrupts or DMA requests are enabled.
### Common Library Functions for STM32 General-Purpose Timers
- **Timer parameter initialization:**
`void TIM_TimeBaseInit(TIM_TypeDef* TIMx, TIM_TimeBaseInitTypeDef* TIM_TimeBaseInitStruct);`
- **Timer enable function:**
`void TIM_Cmd(TIM_TypeDef* TIMx, FunctionalState NewState);`
- **Timer interrupt enable function:**
`void TIM_ITConfig(TIM_TypeDef* TIMx, uint16_t TIM_IT, FunctionalState NewState);`
- **Status flag acquisition and clearing:**
```c
FlagStatus TIM_GetFlagStatus(TIM_TypeDef* TIMx, uint16_t TIM_FLAG);
void TIM_ClearFlag(TIM_TypeDef* TIMx, uint16_t TIM_FLAG);
ITStatus TIM_GetITStatus(TIM_TypeDef* TIMx, uint16_t TIM_IT);
void TIM_ClearITPendingBit(TIM_TypeDef* TIMx, uint16_t TIM_IT);
```
These functions allow developers to configure, control, and monitor the STM32 timer peripherals effectively, making them essential tools for embedded development.
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