Compare two bytes with AND

[pom]

Hello guys,

I want to compare two bytes with each other to know, if they have one of them has a 1 or a 0 in a special bit.

By can-bus I get a byte as information, if various things are switched off or turned on. So every bit gives me a single information. Now I have to read it out.

I tried different possibilities to read out the last two bits:

x = data && (1<<0)
x = data & (1<<0)
x = data && 0x02;
x = data && 0b00000001

Above you can see some of my trys. But none of them or others, I also tried but can't remember, work. Me sending a 0x01 or 0x02 by can, the PIC always reacts as if the second bits of the byte was set.

What would be the right way of solving this problem? I would be very thankful fpor help,

pom

[Ttelmah]

'&&', is 'logical' and. It returns a 'true' if both of the incoming bytes are 'true' (non zero). '&', is bitwise and, and is the function you want. You were very close with your second try, except you are just testing the low bit (you are shifting the 'mask' left by nothing...).
Now your description of what you want, is perhaps not very clear. If you want the last two bits of a value, then you need:

x=data & 0b00000011;

Much clearer to use the 'binary' format to show which bits you are testing.

If you want to know if either incoming value (data, and data1 say) has a bit in one of the other of these locations, then you would need:

x=(data & 0b00000011) || (data1 & 0b00000011);

Here the part 'data & 0b00000011' will evaluate as 'true' if either bit is set, as will the similar statement for data1, and then these are logically 'ored' to give the result fed to 'x'. This will be 'true' if either incoming byte has one of the selected bits set.

Best Wishes

[pom]

Hello,

I tried what Ttelmah told me to do. This is my code:

[treitmey]

Don't re-invent the wheel. Use the bit_test() function

[Ttelmah]

As you say, bit_test is simpler, but the functions as posted should work. What is 'y' declared as?. What is rx_data declared as?.
If you look at the manual entry for 'bit_test', you will find the equivalent function posted using a bit mask, and this is exactly the same masking operation as is being performed. The masking form is 'better' (necessary...), when the bit to be tested is a variable. If the bit is fixed, then bit_test is the more efficient implementation.

Best Wishes

[Mark]

[pom]

Thanks for help! I am really happy because of finishing my project by using the bit_test-function. I have never heard of it before. I think, I will never forget it anymore.

Have a nice day, pom