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Section
03 Part 02 – The AND Instruction |
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“A sane mind should not be guilty of a logical fallacy, yet there are very fine minds incapable of following mathematical demonstrations.” ~Henri Poincare |
Introduction
AND – AND logical
This instruction
will perform AND logical between the source operand and
destination
operand, the
result is saved to the destination operand.
So
what is AND logical?
Let
us take two bits, one from the source operand and one from the destination
operand, and perform
AND logical:
|
source operand |
|
destination operand |
|
Result |
|
|
|
|
|
|
|
0 |
AND |
0 |
= |
0 |
|
0 |
AND |
1 |
= |
0 |
|
1 |
AND |
0 |
= |
0 |
|
1 |
AND |
1 |
= |
1 |
The
idea is that both have to be 1 for the result to be 1. To understand why it’s called AND, you might
need to pretend that 0 is referred to as “false” and 1 is referred to as
“true”. So let’s look at the table
again:
|
source operand |
|
destination operand |
|
Result |
|
|
|
|
|
|
|
False |
AND |
False |
= |
False |
|
False |
AND |
True |
= |
False |
|
True |
AND |
False |
= |
False |
|
True |
AND |
True |
= |
True |
The
description of this logic is; “If the source and the destination is
true, then the result is true”, and that is where the name of the logic comes
from.
Examples
OK,
so down to business, here is an example (we’ll pretend that d0 contains
01234567):
|
andi.b #$E2,d0 |
This
instruction will AND the byte E2
with the byte 67 inside d0. Since this is a binary instruction, E2 and 67 in binary is 1110 0010 and 0110 0111.
|
E2 |
1 |
1 |
1 |
0 |
0 |
0 |
1 |
0 |
|
|
|
|
|
|
|
|
|
|
|
AND |
AND |
AND |
AND |
AND |
AND |
AND |
AND |
AND |
|
|
|
|
|
|
|
|
|
|
|
67 |
0 |
1 |
1 |
0 |
0 |
1 |
1 |
1 |
|
|
|
|
|
|
|
|
|
|
|
= |
= |
= |
= |
= |
= |
= |
= |
= |
|
|
|
|
|
|
|
|
|
|
|
62 |
0 |
1 |
1 |
0 |
0 |
0 |
1 |
0 |
As
you can see in the table, both the source and the destination, must be set to 1 for the result to be 1.
E2 AND 67 = 62
And
so, 62 is saved into d0, d0 now contains 01234562.
You
can AND one register to another:
|
and.w d0,d1 |
You
can AND on memory in various ways too:
|
andi.w #$07FF,$00004000 and.w d0,$00004000 and.l $00004000,d7 |
And
you can do it on memory using the address registers:
|
andi.w #$07FF,(a1) and.w d0,(a3) and.l (a6),d7 |
Of
course, there are things you cannot
do such as AND-ing from one memory directly to
another, or directly to an address register:
|
and.w $00020000,$0002004E andi.w #$3F10,a0 |
AND
Immediate
You
may remember that the “add” and “sub” instructions have this. If the source operand is “immediate”, you must use the instruction “andi”
instead of “and” (where the “i” stands for
immediate):
|
andi.w #$003F,d0 |
Again,
don’t worry if you use just plain “and” instead, as the assembler will turn it
into “andi” for you, when it assembles your code.