Setting Clearing and Copying bits of data
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AND xx will clear the bits in A that are also clear in xx, for example:

       A            xx      after AND xx
   %abcdefgh    %01010101    %0b0d0f0h

ORA xx will set the bits in A that are also set in xx, for example:

       A            xx      after ORA xx
   %abcdefgh    %01010101    %a1c1e1g1

EOR xx will toggle the bits in A that are set in xx, for example:

       A            xx      after EOR xx
   %abcdefgh    %01010101    %aBcDeFgH

To clear the bits in A that are ''set'' in xx, use both ORA and EOR, for
example:


       A            xx      after OR xx  after EOR xx
   %abcdefgh    %01010101    %a1c1e1g1    %a0c0e0g0

You can copy a number of bits to a memory location without changing the
other bits using EOR and AND. For example, to copy the top four bits of A
into a memory location without changing the bottom four bits, use the
following:

                A=12345678  dst=abcdefgh
    EOR dst       ********      abcdefgh
    AND #&F0      ****0000      abcdefgh
    EOR dst       1234efgh      abcdefgh
    STA dst       1234efgh      1234efgh

This is much more efficient than the usual code:

    PHA
    LDA dst:AND #&0F:STA dst
    PLA
    AND #&F0:ORA dst:STA dst