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LDX: Difference between revisions
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==== Cycle Penalties ==== | |||
* In [[direct page addressing]] modes, LDX takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]] modes, LDX takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
* | * | ||
Latest revision as of 06:38, 22 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | A2 | 2/3 bytes | 2 cycles* | ||||
| Absolute | AE | 3 bytes | 4 cycles* | ||||
| Direct Page | A6 | 2 bytes | 3 cycles* | ||||
| Absolute Indexed by Y | BE | 3 bytes | 4 cycles* | ||||
| Direct Page Indexed by Y | B6 | 2 bytes | 4 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| N | . | . | . | . | . | Z | . | |
LDX (Load X) is a 65x instruction that loads a value into the X index register. In immediate addressing only, LDX is a total of 3 bytes long when the index registers are 16 bits wide.
Syntax
LDX #const LDX addr LDX dp LDX addr, Y LDX dp, Y
Cycle Penalties
- In direct page addressing modes, LDX takes another extra cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty, page 463 on LDX
- Labiak, page 150 on LDX
- 7.0 on MCS6500 Manual, page 96 on LDX
- B-18, lbid.
- Carr, page 264 on LDX
- Leventhal, page 3-72 on LDX
- snes9x implementation of LDX: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L772
- undisbeliever on LDX: https://undisbeliever.net/snesdev/65816-opcodes.html#ldx-load-index-register-x-from-memory
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#LDX