Getting Bits out of Bytes

[tom_pay]

Hi

I am trying to get a PIC to send a byte to another PIC via 433MHz transmitters and receivers.

To get them to talk I need to get the specific bits out of a byte.

How can I do this in a quick and efficient manner?

My current coding is:

bit7 = (byte_variable >> 7 ) & 0b1

; ect.


I was hoping to have a sort of thing that could be like this:

byte_variable [ bit number ] = bit7

That way it could be used in a for loop.

Thanks

Tom

 

[ericgibbs]

hi,
You could rotate thru carry and test the carry bit

 

[tom_pay]

Ummm, I am only new to PIC's. Could you please explain that a little further. Sorry!!

Thanks

Tom

 

[ericgibbs]

Ummm, I am only new to PIC's. Could you please explain that a little further. Sorry!!

Thanks

Tom

Hi Tom,
I dont use 'C', but in assembler you would shift the Byte left or right depending which order you want to send the bits; ie ; lsb or msb first.

As the Byte is shifted, test the carry flag for a '1' or '0' and transmit it, do that 8 times for all the bits.

 

[tom_pay]

Ok, that is kinda what I was doing, I think I will settle for that then.

Thanks for your help.

Tom

 

[Pommie]

This will send LSB first,

    for(i=0;i<8;i++){
        bit=(byte_var>>i)&1;
        //do something with bit
    }

MSB first is,

    for(i=7;i<8;i--){
            bit=(byte_var>>i)&1;
            //do something with bit
    }

// a better but less efficient way would be,
    for(i=0;i<8;i++){
        bit=(byte_var>>(7-i))&1;
        //do something with bit
    }

The i<8 in the first example is so i doesn't need to be signed.

Mike.

 

[futz]

This will send LSB first,

    for(i=0;i<8;i++){
        bit=(byte_var>>i)&1;
        //do something with bit
    }

One quick tip: If you're using BoostC you can't use "bit" as a variable because it's reserved as a variable type. That one bit me recently. The error message is vague and doesn't point to the actual problem. Just something to keep in mind.

 

[be80be]

Some compliers will let you do a simple
var.7 = 1 or var.7<>1

Look under Alias and Modifiers in your complier help file