STM8 addressing modes |
PM0044 |
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6.4.5Extended Indexed (only LDF instruction)
The offset is an extended word, thus allowing 16Mbyte addressing space (from 000000 to FFFFFF), but requires 3 bytes after the op-code.
Example: |
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0690 |
AE02 |
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LD |
X,#2 |
0692 |
AF010780 |
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LDF A,(table,X) |
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010780 |
BF |
table |
dc.b |
$BF |
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86 |
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dc.b |
$86 |
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DDFE |
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dc.w |
$DDFE |
Action:
X = 2, A = (table, X) = ($010780,X) = ($010780+2)) = ($010782) = $DD
Figure 15. Far Indexed - 16-bit offset - addressing mode example
LDF A, (table, X)
table . byte BF
LD A, (table, X)
table . byte BF
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Before Completion |
PC |
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AF |
0692 |
0692 |
01 |
0693 |
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07 |
0694 |
X |
80 |
0695 |
02 |
A
Previous Value
BF |
010780 |
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86 |
010781 |
010780 |
02 |
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DD |
010782 |
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Adder |
FE |
010783 |
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EA |
010782 |
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After Completion |
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AF |
0692 |
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X |
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02 |
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01 |
0693 |
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07 |
0694 |
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80 |
0695 |
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New PC |
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0696 |
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0696 |
BF |
010780 |
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86 |
010781 |
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A |
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DD |
010782 |
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DD |
FE |
010783 |
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Steps to determine
Effective Address
PC = 0692
PC = PC + 1 = 0693
EA= (PC):(PC+1):(PC+2)+X = 010780+02 = 010782
Instruction Complete
A = (EA) = DD
New PC = PC+3 = 0696
VR02059R
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Doc ID 13590 Rev 3 |