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Section
01 Part 05 – The MOVE Instruction |
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“Computers are like Old Testament gods; lots of rules and no mercy.” ~Joseph Campbell |
Introduction
MOVE – copy data from source
to destination
You’ve
seen this instruction used multiple times by now in the previous parts, so
let’s look at it in more detail.
This
instruction will copy the number from the source operand and move it to the destination operand, the source operand will remain unchanged.
Examples
Examples
are always good; so we’ll start with moving a byte to a data register:
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move.b #$95,d0 |
This
will copy the byte 95 into data register d0:
As
you can see, no matter what was in d0 before, it will always be replaced with
the byte 95.
Here
are a few more examples:
As you
can see, only the right byte is replaced, the rest remains the same, this is because the instruction had .b telling the processor to move
only a byte.
Here’s
an example using .w for word:
|
move.w #$40F5,d0 |
This
will copy the word 40F5 into data register d0:
As you
can see, no matter what was in d0 before, it will always be replaced with the
word 40F5.
Here
are a few more examples:
As
you can see, only a word
of d0 was replaced, the rest of d0 remains the same,
this is because the instruction had .w
telling the processor to move only a word.
Here’s
an example using .l for long-word:
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move.l #$55667788,d0 |
This
will copy the long-word 55667788 into data register d0:
As
you can see no matter what was in d0, it will always be replaced by
55667788. Because the instruction had .l for long-word, the entire register gets
changed.
Other
Examples
You
can move numbers from one register to another as well, for example:
|
move.w d0,d1 |
This
will copy a word of data from d0
to d1.
The
4567 was copied from d0 over to d1, d0 will still
contain 01234567 though. Remember, the source operand always remains unchanged.
Moving
to and from memory:
|
move.w d0,$0000104E |
This
will copy the word in d0,
and move it into memory at offset $0000104E. If d0 contains 99004980, then 4980
is copied to memory at offsets 0000104E and 0000104F:
|
Offset |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
A |
B |
C |
D |
E |
F |
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etc |
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00001030 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
00001040 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
49 |
80 |
|
00001050 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
00001060 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
etc |
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You can
copy data from memory to a data register:
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move.w $00001062,d0 |
If d0 contains 40414243, and the
data in memory is:
|
Offset |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
A |
B |
C |
D |
E |
F |
|
etc |
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|
00001030 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
00001040 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
00001050 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
00001060 |
00 |
00 |
00 |
22 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
etc |
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0022 is copied to d0, and d0 will
then contain 40410022.
You can
copy from memory to memory:
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move.l $00000800,$00000822 |
This
is moving a long-word, so if the data in memory is:
|
Offset |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
A |
B |
C |
D |
E |
F |
|
etc |
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000007F0 |
00 |
12 |
33 |
00 |
8E |
00 |
00 |
00 |
00 |
00 |
7F |
00 |
00 |
00 |
00 |
00 |
|
00000800 |
00 |
00 |
99 |
1A |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
00000810 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
44 |
00 |
00 |
00 |
00 |
34 |
44 |
45 |
00 |
|
00000820 |
00 |
12 |
34 |
43 |
99 |
08 |
FE |
04 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
etc |
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The
bytes from 00000800, 00000801, 00000802 and 00000803, are copied over to 00000822, 00000823, 00000824 and 00000825:
|
Offset |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
A |
B |
C |
D |
E |
F |
|
etc |
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|
000007F0 |
00 |
12 |
33 |
00 |
8E |
00 |
00 |
00 |
00 |
00 |
7F |
00 |
00 |
00 |
00 |
00 |
|
00000800 |
00 |
00 |
99 |
1A |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
00000810 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
44 |
00 |
00 |
00 |
00 |
34 |
44 |
45 |
00 |
|
00000820 |
00 |
12 |
00 |
00 |
99 |
1A |
FE |
04 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
00 |
|
etc |
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If
you recall on Part 04, we talked about “address registers”.
You
can copy data to memory through the “address registers” too, by indexing, the auto
incrementing/decrementing, and others.
Here
are a few examples just to give you a rough idea of the possibilities:
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move.w (a0),(a1) move.w (a0),d0 move.w d1,(a0)+ move.w d1,$10(a1) move.b #$98,(a0)+ move.l $29(a0),$00120020 move.b $00120020,(a1)+ |