GameBoy Assembly Language Tutor, V1.1, by kOOPa
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 Since books on the Z80 are getting harder & harder to find,
hopefully the information here might be helpful to those
trying to understand assembly language specific to GameBoy.


 AND A    ->    a = a and a,     a = a & a

                This command clears the Carry flag and sets
                the Zero flag if a = 0. A itself is unaffected.

 cp #     ->    NA               NA

                Here # can be a register or immediate byte value.
                A is compared to #. If A = #, Zero flag is set.
                If A < #, Carry is set & Zero is reset.
                If A > #, Carry is reset & Zero is reset.

 or a     ->    a = a or a,      a = a | a

                Same result as 'and a'.
                ('and a' and 'or a' are often used to see if
                a = 0 since they are smaller in size than
                using 'cp 0' to do the same thing.) 

 xor a   ->     a = a xor a,      a = a ^ a

                This command clears the Carry flag and sets
                the Zero flag. A is set equal to zero.
                (This command is often used in place of
                'ld a,0' since it is one byte smaller code.)