Anyone has any idea how to write the coding for an inverse() function in c programming which will only invert or toggle the 4 lower significant bits (a0~a3) and leave the 4 most significant bits (a4~a7) unchanged?

e.g.

porta = 0bx01010000;

and after the inverse function,

porta = inverse(porta);

so porta now is 0b01011111.

any one have any ideas? I've got a headache busting my brains out on this problem...

 

Look into the Exclusive-Or operator "^". Just exclusive-or the binary value 0x00001111 with the byte in which you want to toggle the bits of the lower nibble.

hgmjr

 

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hgmjr