Timer prescaler and clock division in Embedded C - Step-by-Step Execution

Concept Flow - Timer prescaler and clock division

Start Timer

↓

Input Clock Frequency

↓

Apply Prescaler

↓

Divide Clock Frequency

↓

Timer Counts at New Frequency

↓

Timer Overflow or Compare Event

↓

Interrupt or Action Triggered

The timer starts with an input clock frequency, applies a prescaler to slow it down, then the timer counts at this divided frequency until an event triggers.

Execution Sample

Embedded C

uint32_t timer_freq = 16000000;
uint16_t prescaler = 8;
uint32_t timer_tick = timer_freq / prescaler;
// Timer counts at timer_tick frequency

Calculate timer tick frequency by dividing the input clock by the prescaler.

Execution Table

Step	Variable	Value	Action	Result
1	timer_freq	16000000	Set input clock frequency	16 MHz
2	prescaler	8	Set prescaler value	Divide clock by 8
3	timer_tick	timer_freq / prescaler	Calculate timer tick frequency	2000000 Hz
4	Timer Counting	At 2 MHz	Timer increments counter at this rate	Counts every 0.5 microseconds
5	Timer Overflow	When counter reaches max	Timer triggers event	Interrupt or flag set
6	-	-	Stop	Timer runs until stopped or reset

💡 Timer runs continuously until stopped or overflow event triggers

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
timer_freq	undefined	16000000	16000000	16000000
prescaler	undefined	8	8	8
timer_tick	undefined	undefined	2000000	2000000

Key Moments - 3 Insights

Why does the timer frequency decrease after applying the prescaler?

Because the prescaler divides the input clock frequency, slowing down the timer increments as shown in step 3 of the execution_table.

What happens if the prescaler is set to 1?

The timer frequency equals the input clock frequency, so the timer counts at the fastest rate possible, as implied in step 3 where prescaler divides the clock.

How does the timer know when to trigger an event?

When the timer counter reaches its maximum value (overflow), it triggers an event as shown in step 5 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the timer_tick frequency after applying the prescaler?

A 16,000,000 Hz

B 8,000,000 Hz

C 2,000,000 Hz

D 125,000 Hz

💡 Hint

Check step 3 in the execution_table where timer_tick is calculated.

At which step does the timer trigger an event due to overflow?

A Step 5

B Step 4

C Step 2

D Step 6

💡 Hint

Look for the step mentioning timer overflow and event trigger in the execution_table.

If the prescaler is changed from 8 to 4, how does timer_tick change?

A It halves

B It doubles

C It stays the same

D It becomes zero

💡 Hint

Refer to variable_tracker and step 3 in execution_table to see how prescaler affects timer_tick.

Concept Snapshot

Timer prescaler divides the input clock frequency.
Timer frequency = Input clock / Prescaler.
Lower timer frequency means slower counting.
Timer counts until overflow triggers event.
Prescaler controls timer speed easily.

Full Transcript

This visual execution shows how a timer uses a prescaler to divide its input clock frequency. Starting with a 16 MHz clock, applying a prescaler of 8 divides the frequency to 2 MHz. The timer then counts at this slower rate, incrementing every 0.5 microseconds. When the timer counter reaches its maximum value, it triggers an overflow event, which can generate an interrupt or set a flag. Changing the prescaler changes the timer tick frequency inversely. This helps control how fast the timer counts without changing the main clock.