PM0044 |
STM8 addressing modes |
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6.4.2Short Indexed addressing mode
The offset is a byte, thus requires only one byte after the op-code, but only allows 00..1FE addressing space.
Example: |
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0089 |
11223344 |
table dc.l |
$11223344 |
0759 |
AE03 |
LD |
X,#3 |
075B |
E689 |
LD |
A,(table,X) |
Action:
X = 3
A = (table, X) = ($89, X) = ($89, 3) = ($8C) = $44
Figure 12. Short Indexed - 8-bit offset - addressing mode example
Before completion
Table .long 11223344
LD A, (table,X)
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A |
11 |
0089 |
Previous Value |
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22 |
008A |
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X |
33 |
008B |
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03 |
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44 |
008C |
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PC |
E6 |
075B |
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075B |
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89 |
075C |
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075D |
89 |
03 |
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Adder |
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EA |
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008C |
Steps to determine
Effective Address
PC = 075B
PC = PC + 1 = 075C
EA = (PC) + X = 89 + 03 = 008C
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After Completion |
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Table .long 11223344 |
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11 |
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0089 |
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Instruction Complete |
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22 |
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008A |
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A |
A = (EA) = 44 |
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33 |
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008B |
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44 |
New PC = PC + 1 = 075D |
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X |
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44 |
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008C |
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03 |
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LD A, (table,X) |
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075B |
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E6 |
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New PC |
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89 |
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075C |
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075D |
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075D |
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VR02059D |
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Doc ID 13590 Rev 3 |
41/162 |