Where to load ISR in Sketch

In researching the use of ISR’s for motors I have come across two instances (elsewhere) that state the ISR needs to be declared before the rest of the sketch.

ISR
SetUp
Loop
etc

However, when I search the Arduino Forums I cannot find anything to this effect.

Is this true or are there just some misunderstood conceptions out there?

MavenScout: In researching the use of ISR's for motors I have come across two instances (elsewhere) that state the ISR needs to be declared before the rest of the sketch.

ISR SetUp Loop etc

However, when I search the Arduino Forums I cannot find anything to this effect.

Is this true or are there just some misunderstood conceptions out there?

I think someone misunderstood. Or perhaps there was more to the example they were giving. You can generally define an ISR wherever you want. Either they misunderstood what they were doing or you misunderstood what they wrote.

In ancient times the magical incantation that the Arduino IDE used to create function prototypes (so that you didn't have to) would break. When that happened you could fix the immediate problem (function not declared) by moving the function declaration to before where the function was used. In the case of an ISR that typically meant 'before setup()'.

You should not have a problem putting those three functions in any order you like. I typically find it easiest to understand when the order is:

void setup() {

    attachInterrupt(0, MyISR);
}

void MyISR() {
}

void loop() {
}

// Then any functions called by loop()