IF - WHILE and variables

[flotulopex]

Hello,

Trying different ways to make some code more efficient, I found that variables may not be used the same way in IF or WHILE commands.

btn_x = VAR BYTE
btn_x = PORTB & %00111110

if btn_x = 2  then .... => this works

while PORTB & %00111110 = 2 ... => this works too

while btn_X = 2 ... this won't work (?!)

In the case of IF, btn_x variable will be recognised as in the WHILE, it will not as long as I don't write it as in the code above.

I understand the difference between both commands functionalities; it is about to know why they can't be handled the same way.

[Dave]

flotulopex, Some more code would be nice... I havent had any problem with the way you are using them.. Some more code however might solve the problem...

Dave Purola,
N8NTA

[mister_e]

I know what you want to do, but unfortunately you can't do it.

What you want it's something like
MakePORTB CON PORTB & %00111110

but this will not compile. What you may do is use a Macro, but there's no advantage in this case.

btn_x = PORTB & %00111110
Work, but only where it is called.

You may use A timer interrupt to refresh btn_x, but still, there's no real advantages, and you also need another variable to confirm that btn_x have been refreshed.

Assuming you want to poll some push buttons, then yes Timer interrupt could be interesting. That's how I deal with them most of the time.

You can use the timer interrupt to read the push buttons, to confirm that it's not just a glitch and then, to do the debouncing. Now we talk

[mister_e]

btn_x = PORTB & %00111110

If btn_x=2 would mean that the other inputs are all low, but PORTB.1

[tenaja]

btn_x = VAR BYTE
btn_x = PORTB & %00111110

That is a one-time calculation. It never changes in your loop. You've got to update btn_x in the loop if you don't want a never-ending loop.

[flotulopex]

Thank you All.

The program is a "one-shot" reading (it is not a loop).

Using the var is a little less words consuming (5 words) as if I use the full statement "PORTB & %00111110".