Does interrupt service routine in PIC16F877A work with other self-defined variables?

Question

On internet can seen countless simple example like the one below

void __interrupt() isr()
{
  
if(TMR1IF)
   {Do something}

}

But does it work on self-defined variables? As an example, define a bool CurrentMeasurementReady. I can't find similar examples to the one below.

void __interrupt() isr()
{
  
if(TMR1IF&&CurrentMeasurementReady)
   
{Do something}

}

Answer 1

I believe what you are asking about is the scope of variables in the interrupt service routine (ISR).

If CurrentMeasurementReady a declared inside the ISR then it’s scope will be limited to that function, and it will potentially be reinitialized every time the function is called. If CurrentMeasurementReady is declared globally then everyone has access to it and its value is persistent.

Do note that when you’re sharing global variables between the ISR and any other functions you must declare that variable as “volatile”, otherwise the compiler will optimize away certain operations and you will NOT enjoy debugging that. Eg:

volatile bool CurrentMeasurementReady;