GPIO Toggle Calculator

Inputs

Set your target waveform and timer assumptions. Fields accept decimals.

Frequency (Hz) *

Target toggle frequency.

Duty cycle (%) *

Used for PWM timing.

Mode *

Select based on your timer hardware.

Solve for *

Choose which value you know.

Duration (s) *

Used when solving cycles.

Cycles (count) *

Used when solving duration.

MCU clock (MHz) *

Core or timer clock, as applicable.

Prescaler *

Timer clock divider.

Timer width (bits) *

Used to detect count overflow.

Rise time (ns)

Include driver + trace rise time.

Fall time (ns)

Include pull-down + load effects.

Load capacitance (pF)

Pin + wiring + input capacitance.

Series resistance (Ω)

Optional damping resistor.

Reset

Tip: If you need a non-50% duty waveform, keep Mode on PWM.

Example data table

Sample inputs and expected outputs for quick validation.

Frequency (Hz)	Duty (%)	Clock (MHz)	Prescaler	Timer bits	Period (µs)	High (µs)	Low (µs)	PWM TOP
1,000	50	48	1	16	1,000	500	500	47,999
10,000	25	72	8	16	100	25	75	899
100,000	50	120	1	16	10	5	5	1,199

Values assume PWM mode and ideal edges (no quantization rounding).

Formula used

Timing

Period: T = 1 / f
High time: T_H = T · (D/100)
Low time: T_L = T − T_H
Cycles: N = f · t
Edges: E = 2 · N

Timer counts

PWM TOP: TOP = (F_clk / (P · f)) − 1
PWM HIGH compare: CMP ≈ (D/100) · (TOP+1) − 1
Toggle (~50%) OCR: OCR = (F_clk / (2 · P · f)) − 1
Overflow if counts exceed 2^bits−1.

Not all timers implement every mode. Use your datasheet naming.

Edge feasibility estimate uses τ = R · C and budgets about 5τ for near-full transitions.

How to use this calculator

Enter your target frequency and desired duty cycle.
Choose a timer mode: PWM for any duty, or toggle for a fast 50% square wave.
Set MCU clock, prescaler, and timer width to match your design.
Pick whether you know duration or cycles, then enter that value.
Optionally add rise/fall and RC load values to sanity-check feasibility.
Press Calculate. Results appear above the form, with export buttons.

Timing targets and measurable outputs

GPIO toggling is usually specified by frequency and duty cycle, but validation requires measurable quantities. This calculator converts frequency into period, then splits the period into high and low time from the duty percentage. It also reports cycle count and edge count for the selected duration or cycle target, so firmware logs can be compared to oscilloscope captures and automated test limits. For embedded validation, engineers can mirror these computed values in unit tests, ensuring firmware, timer registers, and measured waveforms remain aligned across releases consistently during integration.

Timer configuration planning with counts

Microcontroller timers generate stable waveforms when the required counts fit inside the timer register width. The tool estimates PWM TOP and compare counts using the selected clock and prescaler, and flags overflow when the result exceeds 2^bits−1. It also shows an effective frequency derived from floored counts, plus error in parts per million, supporting quick prescaler selection for a tighter match.

Toggle versus PWM mode tradeoffs

Many designs need a 50% square wave clock, while others need asymmetric duty for LEDs, step inputs, or protocol timing. Toggle-on-compare mode is efficient and can reach high rates, but it naturally produces near-50% duty. PWM mode allows arbitrary duty values and provides explicit high and low timing. The calculator keeps both sets of timer results visible to simplify mode selection early.

Edge integrity and loading estimates

At higher frequencies, rise and fall times become a significant fraction of the period, reducing valid logic margins. The calculator compares the computed high and low time against the provided rise and fall times and warns when transitions dominate. A simple RC model uses τ=R·C to estimate a practical edge budget, producing a rough maximum frequency indicator for long traces, capacitive inputs, or added series resistors.

Documentation, exports, and repeatable testing

Engineering workflows often require traceability across revisions. After calculation, the export buttons generate a CSV key-value summary and a one-page PDF report that can be attached to lab notes, build tickets, or validation records. The example table provides reference scenarios to confirm tool behavior, while warnings highlight conditions that typically lead to failed timing checks or distorted waveforms.

FAQs

1) What is the difference between toggle and PWM modes?

Toggle mode flips the pin on each compare match, producing an approximate 50% duty square wave. PWM mode sets and clears the pin within one timer period, allowing a configurable duty cycle and explicit high and low timing.

2) Why does the calculator show “effective frequency” and ppm error?

Timer registers must be integers, so the ideal count is rounded down. The effective frequency reflects the rounded count, and the ppm value quantifies how far the real output will deviate from the target.

3) What should I do when TOP or OCR overflows?

Increase the prescaler, reduce the target frequency, or select a wider timer. Any of these changes reduces the required count value so it fits within the timer’s maximum register range.

4) How do rise and fall times affect timing validity?

If rise time approaches the high interval, the signal may not reach a stable logic high. If fall time approaches the low interval, it may not reach a stable logic low. The tool warns when these margins are tight.

5) Is the RC frequency limit an exact specification?

No. It is a conservative estimate based on a simple τ=R·C model and a typical “about 5τ” transition budget. Use it for early design screening, then confirm with measurement or detailed simulation.

6) Why are exports available only after running a calculation?

The CSV and PDF are built from the most recent computed result stored in the session. This ensures exported files match the exact inputs and outputs used for your current design snapshot.