PM0044 |
STM8 addressing modes |
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6.13Bit Direct (Long) addressing mode
Table 37. |
Overview of Bit Direct addressing mode instruction |
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Addressing mode |
Syntax |
EA formula |
Ptr Adr |
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Dest adr |
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Long Direct |
longmem, #pos |
(longmem) |
op + 1..2 |
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Word |
0000..FFFF |
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The data byte required for the operation is found by its memory address, which follows the op-code. The bit used for the operation is selected by the bit selector which is encoded in the instruction op-code.
Table 38. Available Bit Direct instructions
Instructions |
Functions |
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BRES |
Bit Reset |
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BSET |
Bit Set |
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BCPL |
Bit Complement |
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BCCM |
Copy Carry Bit to Memory |
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The address is a word, thus allowing 0000 to FFFF addressing space, but requires 2 bytes after the op-code. The bit selector #n (n=0 to 7) selects the nth bit from the byte pointed to by the address.
Example: |
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0408 |
721006E5 |
BCPL |
coeff, #0 |
06E5 |
40 |
coeff dc.b |
$ 40 |
Action: |
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(coeff) = ($06E5) XOR 2**0 = $40 XOR $01 = $41
Doc ID 13590 Rev 3 |
57/162 |
STM8 addressing modes |
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Figure 22. Bit Long Direct addressing mode example |
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Before c ompletion |
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PC |
Steps to d etermine |
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effective address |
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BCPL Coeff,#0 |
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90 |
0408 |
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0408 |
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10 |
0409 |
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PC = 0408 |
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06 |
040A |
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06E5 |
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PC = PC + 2 = 040A |
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EA = (PC ) :(PC+1) = 06E5 |
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E5 |
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040B |
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040C |
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Coeff .byte 040h |
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EA |
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40 |
06E5 |
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06E5 |
EA = (PC ): (PC+1) = 06E5 |
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After c ompletion |
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BCPL Coeff,#0 |
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0408 |
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90 |
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Instruction c omplete |
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10 |
0409 |
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(EA) = (EA) | 2**0 = 40 | 01 = 41 |
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06 |
040A |
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New PC = PC + 2 = 040C |
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E5 |
040B |
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New PC |
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040C |
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040C |
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Coeff .byte 040h |
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41 |
06E5 |
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40 XOR 01 |
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58/162 |
Doc ID 13590 Rev 3 |