PIC Microcontroller Timer & Delay Calculator
8-Bit (Timer0/2)
16-Bit (Timer1/3)
1
2
4
8
16
32
64
128
256
Calculation Results
Understanding PIC Microcontroller Timer Calculations
Microchip PIC microcontrollers use internal timers to manage operations like PWM generation, periodic interrupts, and time-sensitive tasks. To use these timers effectively, developers must calculate the precise "Preload Value" to write into the timer registers (TMRxH and TMRxL).
The Core Formula
The internal clock of a PIC microcontroller (Fcy) is typically the Oscillator Frequency (Fosc) divided by 4. The timer increments every instruction cycle, modified by a prescaler.
Instruction Cycle (Tcy) = 4 / Fosc
Timer Ticks = Desired Delay / (Tcy * Prescaler)
Preload Value = (Max Timer Value + 1) – Timer Ticks
Timer Ticks = Desired Delay / (Tcy * Prescaler)
Preload Value = (Max Timer Value + 1) – Timer Ticks
Key Parameters
- Fosc (MHz): The frequency of your crystal oscillator or internal clock source.
- Prescaler: A hardware clock divider that slows down the timer increment rate. Common values are 1:2, 1:8, or 1:256.
- Bit Depth: 8-bit timers count up to 255 (256 total steps), while 16-bit timers count up to 65,535 (65,536 total steps).
Practical Example
Suppose you are using a 4MHz Crystal and you want a 10ms delay using a 16-bit timer with an 1:8 prescaler:
- Instruction Cycle = 4 / 4,000,000 = 1 microsecond.
- Effective Tick Rate = 1µs * 8 (Prescaler) = 8 microseconds.
- Ticks needed = 10ms (10,000µs) / 8µs = 1,250 ticks.
- Preload Value = 65,536 – 1,250 = 64,286.
- Convert to Hex: 0xFB1E.
Loading 0xFB into TMRxH and 0x1E into TMRxL will trigger an interrupt exactly every 10 milliseconds.