Pin check issue

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warren1
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#1
Posted by warren1: Fri. Jul 6, 2012 - 02:11 AM
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Ok im not sure why the pin check in the if statement doesn't work. It works fine by itself but not as in the statement below. Can someone tell me why?

im trying to create something like:

if((1 & 1) != 0)
{
		//Do work	
}

	uint8_t Check = 0b00000001

	if((PORTB & _BV( PB7 ) & (Check & (1<<0))) != 0)
	{
		//Do work
	}

[/code]

Tags:

AVR Microcontrollers, megaAVR and tinyAVR
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Koshchi
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Posted by Koshchi: Fri. Jul 6, 2012 - 02:42 AM
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You need to use PINB, not PORTB.

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larryvc
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Posted by larryvc: Fri. Jul 6, 2012 - 02:48 AM
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Try this. I like parens.

	if (((PINB & _BV(PB7)) && (Check & (1 << 0))) != 0)
   {
		//Do work
	}

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Kartman
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Posted by Kartman: Fri. Jul 6, 2012 - 03:53 AM
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I think you want && between to two statements. As written, the result would evaluate to:
0x80 & 0x01 = 0x00
or
0x00 & 0x01 = 0x00

Thus we can see that the result will never be non-zero.
Using a logical and (&&) it would evaluate as:

true && true = true
false && true = false

This is a common mistake - never confuse bit wise operators with logical operators.

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warren1
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Posted by warren1: Fri. Jul 6, 2012 - 04:43 AM
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Thanks Koshchi, larryvc & Kartman. I didn't know you could use a PINx command and i wasn't aware about &&.

So
& is bit wise
&& is logical operators (truth table of AND)

Cool.

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larryvc
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Posted by larryvc: Fri. Jul 6, 2012 - 05:01 AM
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warren1 wrote:
Cool.
Yeah. :wink:

"I may make you feel but I can't make you think" - Jethro Tull - Thick As A Brick

"void transmigratus(void) {transmigratus();} // recursio infinitus" - larryvc

"It's much more practical to rely on the processing powers of the real debugger, i.e. the one between the keyboard and chair." - JW wek3

"When you arise in the morning think of what a privilege it is to be alive: to breathe, to think, to enjoy, to love." -  Marcus Aurelius

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Bronze MarkJohanEkdahl
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Posted by JohanEkdahl: Fri. Jul 6, 2012 - 07:08 AM
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Quote:

I didn't know you could use a PINx

In the context give, it is not "could" but "must".

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ka7ehk
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Posted by ka7ehk: Fri. Jul 6, 2012 - 05:30 PM
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The PINn register tells you the logic state of what the pins actually ARE.

If its an output, PORTn tells you the logic state that you told it to be. If is an input, it tells you whether pull-ups are on or off.

Jim

 

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