Timer prescaler and clock division in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Calculate Timer Frequency with Prescaler

Given a microcontroller clock frequency of 16 MHz and a timer prescaler set to 64, what is the timer's input clock frequency?

Embedded C

unsigned long clock_freq = 16000000;
unsigned int prescaler = 64;
unsigned long timer_freq = clock_freq / prescaler;
printf("%lu\n", timer_freq);

A 250000

B 1000000

C 64000000

D 16000000

💡 Hint

Divide the main clock frequency by the prescaler value.

The timer frequency is the main clock frequency divided by the prescaler. 16,000,000 / 64 = 250,000 Hz.

❓ Predict Output

intermediate

Timer Overflow Period Calculation

If a timer counts from 0 to 255 (8-bit timer) with a clock frequency of 1 MHz after prescaling, what is the overflow period in microseconds?

Embedded C

unsigned long timer_clock = 1000000;
unsigned int max_count = 256;
unsigned long overflow_period = max_count * (1000000 / timer_clock);
printf("%lu\n", overflow_period);

A 1000000

B 255

C 1

D 256

💡 Hint

Overflow period = max count * timer clock period.

Timer counts 256 steps at 1 MHz clock, so overflow period = 256 * 1 microsecond = 256 microseconds.

🔧 Debug

advanced

Identify the Error in Prescaler Setting Code

What error will occur when compiling this code snippet that sets a timer prescaler?

Embedded C

unsigned int prescaler = 8;
TCCR0B = (1 << CS01) | (1 << CS00);

A SyntaxError: missing semicolon after prescaler declaration

B TypeError: invalid bitwise operation

C No error, code compiles successfully

D RuntimeError: invalid prescaler value

💡 Hint

Check punctuation at the end of statements.

The first line is missing a semicolon, causing a syntax error.

❓ Predict Output

advanced

Effect of Clock Division on Timer Frequency

If the main clock is 8 MHz and the timer uses a clock division factor of 256, what is the timer frequency?

Embedded C

unsigned long main_clock = 8000000;
unsigned int division_factor = 256;
unsigned long timer_freq = main_clock / division_factor;
printf("%lu\n", timer_freq);

A 256

B 31250

C 8000000

D 32768

💡 Hint

Divide the main clock by the division factor.

8,000,000 / 256 = 31,250 Hz timer frequency.

🧠 Conceptual

expert

Understanding Combined Prescaler and Timer Resolution

A 16-bit timer runs with a 20 MHz clock and a prescaler of 128. What is the maximum timer overflow period in milliseconds?

A 655.36 ms

B 1310.72 ms

C 419.43 ms

D 1638.4 ms

💡 Hint

Calculate timer clock frequency, then multiply by max count (65536) and convert to milliseconds.

Timer clock = 20,000,000 / 128 = 156,250 Hz. Period = 1/156,250 = 6.4 µs. Max count = 65536. Overflow period = 65536 * 6.4 µs = 419,430.4 µs = 419.43 ms.