[A83] Re: How using and

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[A83] Re: How using and


The logical operation AND works like this:

Source | Mask  | Result:
-------+-------+--------
   0   |   0   |  0
   1   |   0   |  0
   0   |   1   |  0
   1   |   1   |  1

AND performs the logical operation AND on each bit of the byte:
10101010 and 11110000 = 10100000

You can't do AND DE, because DE is 2 bytes long, not 1, but you can do AND 
E, which ANDs A with E.  (D is ignored)

Also, the instruction AND A does the same thing as CP 0  (so does OR A)


If you really need to do a 16-bit AND, then you should put the variable into 
HL, then put the mask into de, then:

;HL = HL AND DE
  ld a,l
  and e
  ld l,a
  ld a,h
  and d
  ld h,a




Finally, if you just want to see if 2 16-bit values are both 0, then do 
this:

  ld hl,(var1)
  ld de,(var2)
  xor a
  or h
  or l
  or d
  or e
;Z flag if zero, NZ if not

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