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Section
04 Part 10 – Homework Results 04 |
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“A good essay is 10% inspiration, 15% perspiration, and 75%
desperation.” ~Unknown author |
Introduction
I
left with you a list using a load of instructions explained in this section, so
you could try and work out what d0 contained afterwards. So let’s see how well you did.
Results
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move.w #$0010,d0 mulu.w #$0003,d0 neg.w d0 ext.l d0 asr.l #$01,d0 ror.w #$01,d0 ext.l d0 divu.w #$0002,d0 |
d0 starts with 00000000.
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move.w #$0010,d0 |
d0 now contains 00000010.
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mulu.w #$0003,d0 |
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0010 x 0003 = 00000030 |
d0 now contains 00000030.
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neg.w d0 |
0030 is changed to -0030 (FFD0). Now d0
contains 0000FFD0.
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ext.l d0 |
The word FFD0 inside d0 is extended to long-word, currently d0 contains:
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0000 0000
0000 0000 1111 1111
1101 0000 |
The
MSB of FFD0 is 1 (set), so d0 is extended to:
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1111 1111
1111 1111 1111 1111
1101 0000 |
Now d0 contains FFFFFFD0.
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asr.l #$01,d0 |
d0 contains FFFFFFD0 in binary:
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1111 1111
1111 1111 1111 1111 1101 0000 |
Arithmetically
shifting right by 1 will give us:
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> 1111 1111
1111 1111 1111 1111 1110 1000 > |
Now d0 contains FFFFFFE8.
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ror.w #$01,d0 |
The
word FFE8 of d0 is now rotated right by 01 bit:
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> 0111 1111 1111
0100 v ^ < < < < <
< < < < < < |
Now d0 contains FFFF7FF4.
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ext.l d0 |
The word 7FF4 inside d0 is extended to long-word, currently d0 contains:
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1111 1111
1111 1111 0111 1111 1111
0100 |
The
MSB of 7FF4 is 0 (clear), so d0 is extended to:
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0000 0000
0000 0000 0111 1111 1111
0100 |
Now d0 contains 00007FF4.
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divu.w #$0002,d0 |
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00007FF4 ÷ 0002 = 3FFA r0000 |
Now d0 contains 00003FFA.
And
there is your answer, d0 contains 00003FFA afterwards. Please remember, I don’t expect you to work these
all out in your head, if you’d prefer to use a calculator, that’s fine. The purpose of these homework(s) is to ensure
that you understand how the instructions work individually. They’re not here to test your mathematics.