STM8 addressing modes |
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Figure 7. Immediate addressing mode example
Before Completion
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A |
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Previous Value |
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PC |
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LD A, #0F8h |
A6 |
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05BE |
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05BE |
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F8 |
05BF |
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05C0 |
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Steps to Determine Effective Address
PC = 05BE
PC = PC + 1 = 05BF EA = PC = 05BF New PC = PC + 1
= 05C0
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After Completion |
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A |
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F8 |
A6 |
05BE |
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F8 |
05BF |
New PC |
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05C0 |
05C0 |
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Instruction Complete
A = (EA) = F8
New PC = 05C0
VR02059A
6.3Direct addressing mode (Short, Long, Extended)
Table 20. |
Overview of Direct addressing mode instructions |
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Addressing mode |
Syntax |
EA formula |
Ptr Adr |
Ptr Size |
Dest adr |
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Short |
Direct |
shortmem |
(shortmem) |
op + 1 |
Byte |
00..FF |
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Long |
Direct |
longmem |
(longmem) |
op + 1..2 |
Word |
0000..FFFF |
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Extended |
Direct |
extmem |
(extmem) |
op + 1..3 |
Ext word |
000000..FFFFFF |
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The data byte required for the operation is found by its memory address, which follows the op-code.
Direct addressing mode is made of three sub-modes:
Table 21. Available Long and Short Direct addressing mode instructions
Instructions |
Functions |
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LD, LDW |
Load |
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CP |
Compare |
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AND, OR, XOR |
Logical Operations |
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ADC, ADD, SUB, SBC, ADDW, SUBW |
Arithmetic Addition/Subtraction operations |
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BCP |
Bit Compare |
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34/162 |
Doc ID 13590 Rev 3 |
PM0044 |
STM8 addressing modes |
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Table 21. Available Long and Short Direct addressing mode instructions |
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Instructions |
Functions |
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MOV |
Move |
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CLR |
Clear |
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INC, DEC |
Increment/Decrement |
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TNZ |
Test Negative or Zero |
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CPL, NEG |
1’s or 2’s Complement |
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SLA, SLL, SRL, SRA, RLC, RRC |
Shift and Rotate Operations |
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SWAP |
Swap Nibbles |
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CALL, JP |
Call or Jump subroutine |
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Table 22. Available Extended Direct addressing mode instructions
Instructions |
Function |
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CALLF, JPF |
Call or Jump FAR subroutine |
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LDF |
Far load |
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Table 23. Available Long Direct addressing mode instructions
Instructions |
Function |
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EXG |
Exchange |
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PUSH, POP |
Stack operation |
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Doc ID 13590 Rev 3 |
35/162 |