Embedded calculator, part of Premium
MCU timer & PWM
A timer counts clock ticks: the prescaler slows them, the reload says how many.
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The example, worked out
Given
- Timer clock
- 16 MHz
- Counter width
- 16 bits
- Prescaler
- Pick for me (finest)
- I want
- A frequency
- Frequency
- 1 kHz
Working
- ticks per period
- the counter goes from 0 to ARR, that is N ticks
- what you really get
Results
The formulas
- N = fclk / (P × f)ticks per period
- ARR = round(N) − 1the counter runs from 0 to ARR
- PWM bits = log2(ARR + 1)the duty resolution at that frequency
The usual traps
- Writing the prescaler without the minus one.
- A small count weighs one tick heavily: pick the smallest prescaler that fits.
Questions
How do I set the prescaler and reload of a microcontroller timer?
N = fclk / (P × f): ticks per period. ARR = round(N) − 1: the counter runs from 0 to ARR. PWM bits = log2(ARR + 1): the duty resolution at that frequency.
What does it give for typical values?
÷ 1, reload 15999 for 1 kHz on 16 MHz (0 % off). Prescaler: ÷ 1; Reload (top) value: 15,999.
What are the usual mistakes?
Writing the prescaler without the minus one. A small count weighs one tick heavily: pick the smallest prescaler that fits.
In the app
Your circuit, drawn live
Change a value: the schematic redraws with your numbers on the parts.
The part you can buy
Results rounded to standard values (E12, E24, E96) and power ratings.
The working, shown
Every step written out. Try it first by hand, then check.
Into your notebook
One click puts the circuit on a sheet of your project.
Open the calculatorOpens in the app on 1 December, with Circuit Notebook 1.0
Also in Embedded
- ADC resolution The size of one step, the ideal SNR, what a measured SNR is worth in bits.
- 555 timer Astable frequency and duty, or the pulse of a monostable.