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#Pic18f4550 simple delay how to
#Pic18f4550 simple delay software

After completing the purpose of the interrupt, we need to clear the interrupt flag T0IF in software and load the preload value to the TMR0 register to be ready for the next interrupt. Inside the ISR we will be toggling the RB0 bit for demonstration purpose. Here we require the ISR to execute every second.

The Interrupt Service Routine(ISR) or Interrupt Vector is a code sequence that is executed when an interrupt occurs. I am trying to generate delay of variable length using delay function in MPLAB X IDE for PIC18F4550.

Thus the prescale and preload value should be loaded as we designed. Thus the preload value, TMR0 can be calculated as TMR0 = Resolution - (( T * Fosc ) / (4 * Prescale))

TMR0 – is the timer preload value ( TMR0H, TMR0L ).

Resolution – is the maximum value of the timer ( 0xFFFF H ) As the name suggest, this project is a simple Voltmeter which can measure Voltage.

Prescale – is the maximum prescale value ( T0CON ).

Fosc – is the oscillator frequency (20 MHz).

To calculate the preload value for a 1-second delay at 20Mhz we use the equation, Since the time interval required is large, we will use the prescale value as 256. Here we will be setting up the interrupt to repeat every second. To configure timer interval, we have to specify the prescale and preload value while enabling Timer 0 with the T0CON and TMR0 registers as seen in our previous chapter Timer Delay Implementation in PIC18F4550. Since we will be using the Timer 0 for the interrupt, we have to enable the Global Interrupt Enable (GIE) bit and the Timer 0 Overflow Interrupt Enable (TMR0IE) bit.

TMR0IF: TMR0 Overflow Interrupt Flag bit. If we want to implemet a delay of 1 second using timer 0 with 8MHz, 16 bit mode and pre-scale of 32 we have: 1s (4/8M) 32 (FFFF-TMR0) 1 no need for counter So TMR0 0X0BDB Note that max delay is 8.

Enables the TMR0 overflow interrupt when set

TMR0IE: TMR0 Overflow Interrupt Enable bit.

Timer Interrupt Configurationīefore setting up the timer, we have to enable the interrupt with the INTCON register as seen in our previous chapter Interrupt Handling in PIC18F4550.

#Pic18f4550 simple delay how to

Here we will learn how to set up a timer interrupt to trigger an event at a specific time interval. A timer used as an interrupt enhances this feature by freeing precious processor time used to poll for the timer overflow flag. A Timer is generally used for delay purposes or to trigger a particular event after a defined time interval as discussed in our previous chapter Timer and Counter with PIC18F4550.