Timer prescaler and clock division in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a timer prescaler in embedded systems?

A timer prescaler is a hardware feature that divides the input clock frequency by a set value to slow down the timer counting speed. It helps to measure longer time intervals without changing the main clock.

beginner

How does clock division affect timer operation?

Clock division reduces the frequency of the clock signal fed to the timer by dividing it by a fixed number. This makes the timer count slower, allowing it to measure longer durations or lower frequencies.

intermediate

Why do we use prescalers instead of changing the main clock frequency?

Changing the main clock frequency affects the whole system and can cause instability. Using a prescaler only slows down the timer clock, keeping the rest of the system stable and running at the desired speed.

intermediate

In embedded C, how do you typically set a timer prescaler?

You set a timer prescaler by writing a value to a specific register of the timer peripheral. For example, setting bits in a TIMx_PSC register to divide the clock by a chosen factor.

beginner

If a timer input clock is 16 MHz and the prescaler is set to 7999, what is the timer counting frequency?

The timer frequency = 16 MHz / (7999 + 1) = 16 MHz / 8000 = 2000 Hz. The timer counts 2000 times per second.

What does a timer prescaler do?

A Divides the input clock frequency to slow down the timer

B Increases the timer counting speed

C Changes the main system clock frequency

D Resets the timer counter

A prescaler divides the input clock frequency, slowing down the timer counting speed.

Why is using a prescaler better than changing the main clock frequency?

A Changing main clock is easier

B Prescaler increases system speed

C Prescaler resets the timer

D Prescaler only affects the timer, keeping system stable

Using a prescaler affects only the timer clock, so the rest of the system remains stable.

If the main clock is 8 MHz and prescaler is 7999, what is the timer frequency?

A 8 kHz

B 1 kHz

C 1000 Hz

D 8000 Hz

Timer frequency = 8 MHz / (7999 + 1) = 8 MHz / 8000 = 1 kHz.

Which register is commonly used to set the prescaler in embedded C timers?

A TIMx_PSC

B TIMx_CNT

C TIMx_ARR

D TIMx_CR1

TIMx_PSC register holds the prescaler value for the timer.

What happens if you set the prescaler to 0?

A Timer counts twice as fast

B Timer stops counting

C Timer counts at full input clock speed

D Timer resets automatically

Prescaler 0 means divide by 1, so timer counts at full input clock speed.

Explain what a timer prescaler is and why it is useful in embedded systems.

Think about how slowing the timer clock helps measure time without changing the whole system speed.

Describe how you would calculate the timer counting frequency given the main clock and prescaler value.

Remember the prescaler divides the clock by (value + 1).