This post provides the timer0 code for PIC16F84A microcontroller. This code is written in C language using MPLAB with HI-TECH C compiler. You can download this code from the ‘Downloads‘ section at the bottom of this page.
It is assumed that you know how to blink an LED with PIC16F84A microcontroller. If you don’t then please read this page first, before proceeding with this article.
The result of simulating the code in Proteus is shown below.
In this circuit, PIC16F84A is running on external crystal of 20MHz value. RA0 pin is toggled every time timer0 expires and executes it’s ISR code. In the above figure, it is clear that after approximately every 100usec, RA0 pin is toggled i-e timer0 expires. You can easily change this value in the code.
The code used to initialize timer0 is shown below.
In this function, OPTION_REG is initialized to make timer0 prescalar to be 1:2. Timer0 is an 8bit timer, so it expires after reaching a value of 255. When timer0 prescalar is made 1:2 then it means that timer0 value will increment after every two clock cycles. Since PIC16F84A is running at 5MIPS speed, this means that timer0 will expire after every 256*2/5 = 102 usec. T0IE bit enables timer0 interrupts and GIE bit enables global interrupts.
Timer0 interrupt service routine code is shown below.
Timer0 code for PIC16F84A was compiled in MPLAB v8.85 with HI-TECH C v9.83 compiler and simulation was made in Proteus v7.10. To download code and Proteus simulation click here.
For more detail: PIC16F84A timer0 code and Proteus simulation