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LDX: Difference between revisions
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'''LDX''' (Load X) is a 65x instruction that loads the [[X index register]]. In [[immediate addressing]] only, LDX is a total of 3 bytes long when the index registers are 16 bits wide. | '''LDX''' (Load X) is a 65x instruction that loads 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 ==== | |||
<pre> | |||
LDX #const | |||
LDX addr | |||
LDX dp | |||
LDX addr, Y | |||
LDX dp, Y | |||
</pre> | |||
===== Cycle Penalties ===== | ===== Cycle Penalties ===== | ||
Revision as of 22:39, 6 July 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | A2 | 2 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 | |
| . | . | . | . | . | . | |||
LDX (Load X) is a 65x instruction that loads 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: https://archive.org/details/0893037893ProgrammingThe65816/page/n489
- Labiak page 150 on LDX: https://archive.org/details/Programming_the_65816/page/n160
- MCS6500 Manual page 96 on LDX: https://archive.org/details/mos_microcomputers_programming_manual/page/n114
- https://archive.org/details/mos_microcomputers_programming_manual/page/n219, lbid.
- Carr page 264 on LDX: https://archive.org/details/6502UsersManual/page/n277
- Leventhal page 3-72 on LDX: https://archive.org/details/6502-assembly-language-programming/page/n121
- 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