Difference between revisions of "LDA"
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| − | '''''LDA (Load Accumulator With Memory)''''' is probably the most-used [[opcode]] in 6502 assembly as it loads the most-used register, the [[accumulator]], with memory. | + | '''''LDA (Load Accumulator With Memory)''''' is probably the most-used [[opcode]] in 6502 assembly as it loads the most-used register, the [[Accumulator Register|accumulator]], with memory. |
==Operation== | ==Operation== | ||
This pseudo C code shows how the LDA opcode functions. | This pseudo C code shows how the LDA opcode functions. | ||
| − | SET_NEGATIVE(Operand); // Clears the | + | SET_NEGATIVE(Operand); // Clears the [[Negative Flag]] if the Operand is $#00-7F, otherwise sets it. |
| − | SET_ZERO(Operand); // Sets the | + | SET_ZERO(Operand); // Sets the [[Zero Flag]] if the Operand is $#00, otherwise clears it. |
ACCUMULATOR = Operand; // Stores the Operand in the Accumulator Register. | ACCUMULATOR = Operand; // Stores the Operand in the Accumulator Register. | ||
Revision as of 17:08, 23 May 2013
| Load Accumulator With Memory | ||||||
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LDA (Load Accumulator With Memory) is probably the most-used opcode in 6502 assembly as it loads the most-used register, the accumulator, with memory.
Operation
This pseudo C code shows how the LDA opcode functions.
SET_NEGATIVE(Operand); // Clears the Negative Flag if the Operand is $#00-7F, otherwise sets it. SET_ZERO(Operand); // Sets the Zero Flag if the Operand is $#00, otherwise clears it. ACCUMULATOR = Operand; // Stores the Operand in the Accumulator Register.
Addressing Modes
| Addressing Mode | Assembly Language Form | Opcode | # Bytes | # Cycles |
|---|---|---|---|---|
| Immediate | LDA #Operand | A9 | 2 | 2 |
| Zero Page | LDA Operand | A5 | 2 | 3 |
| Zero Page, X | LDA Operand, X | B5 | 2 | 4 |
| Absolute | LDA Operand | AD | 3 | 4 |
| Absolute, X | LDA Operand, X | BD | 3 | 4* |
| Absolute, Y | LDA Operand, Y | B9 | 3 | 4* |
| (Indirect, X) | LDA (Operand, X) | A1 | 2 | 6 |
| (Indirect), Y | LDA (Operand), Y | B1 | 2 | 5* |
| * Add 1 if page boundary is crossed. | ||||
