PM0044 |
STM8 addressing modes |
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6.9Short Pointer Indirect Long Indexed addressing mode
The pointer address is a byte, the pointer size is a word, thus allowing up to 128 KB addressing space, and requires 1 byte after the op-code.
Example: |
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0089 |
0800 |
ptr dc.w |
table |
0800 |
10203040 table dc.b |
$10,$20,$30,$40 |
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0690 |
AE03 |
LD |
X,#3 |
0692 |
92D689 |
LD |
A,([shortptr.w],X) |
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X = 3 |
A = ([shortptr.w],X) = ((shortptr.w), X) = (($89.w), 3)
= ($0800,3) = ($0803) = $40
Doc ID 13590 Rev 3 |
49/162 |
STM8 addressing modes |
PM0044 |
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Figure 18. Short Pointer Indirect Long Indexed addressing mode example
Before completion
ptr .word table |
08 |
0089 |
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00 |
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008A |
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PC |
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LD A,([shortptr.w],X) |
92 |
0692 |
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0692 |
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D6 |
0693 |
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89 |
0694 |
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X |
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03 |
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table .byte 0x10,0x20,0x30, |
10 |
800 |
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A |
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0x40 |
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20 |
801 |
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Previous value |
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30 |
802 |
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40 |
803 |
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800 |
03 |
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Adder |
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Steps to determine
Effective Address
PC = 0692
PC = PC + 2 = 0694
EA = ((PC)) : ((PC)+1) + X EA = 0803
EA |
0803 |
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After completion |
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ptr .word table |
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08 |
0089 |
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Instruction Complete |
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00 |
008A |
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X |
A = (EA) = 40 |
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New PC = PC + 1 = 0695 |
LD A,([shortptr.w],X) |
92 |
0692 |
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D6 |
0693 |
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New PC |
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89 |
0694 |
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table .byte 0x10,0x20,0x30 |
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0695 |
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0695 |
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10 |
0800 |
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0x40 |
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20 |
0801 |
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30 |
0802 |
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A |
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40 |
0803 |
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40 |
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50/162 |
Doc ID 13590 Rev 3 |