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ROL: Difference between revisions
From SnesLab
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==== Cycle Penalties ==== | |||
* Except in [[accumulator addressing]], ROL takes two extra cycles when the accumulator is 16 bits wide. | * Except in [[accumulator addressing]], ROL takes two extra cycles when the accumulator is 16 bits wide. | ||
* In [[direct page addressing]] modes, ROL takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]] modes, ROL takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
Latest revision as of 17:44, 23 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Accumulator | 2A | 1 byte | 2 cycles | ||||
| Absolute | 2E | 3 bytes | 6 cycles* | ||||
| Direct Page | 26 | 2 bytes | 5 cycles* | ||||
| Absolute Indexed by X | 3E | 3 bytes | 7 cycles* | ||||
| Direct Page Indexed by X | 36 | 2 bytes | 6 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| N | . | . | . | . | . | Z | C | |
ROL (Rotate Left) is a 65x instruction that rotates a value and the carry flag left one bit. The most significant bit is shifted into the carry flag. The carry flag is shifted into the least significant bit.
- When the accumulator is 8 bits wide, 9 bits are rotated.
- When the accumulator is 16 bits wide, 17 bits are rotated.
Syntax
ROL ROL A ROL addr ROL dp ROL addr, X ROL dp, X
Cycle Penalties
- Except in accumulator addressing, ROL takes two extra cycles when the accumulator is 16 bits wide.
- In direct page addressing modes, ROL takes another extra cycle if the low byte of the direct page register is nonzero.
The arrow in the Carr textbook diagram does not circle back around.
See Also
External Links
- Eyes & Lichty, page 490 on ROL
- lbid page 190 before & after diagram of ROL
- Labiak, page 174 on ROL
- 10.3 on MCS6500 Manual, page 149 on ROL
- Carr, page 269 on ROL
- Leventhal, page 3-85 on ROL
- snes9x implementation of ROL: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1011
- undisbeliever on ROL: https://undisbeliever.net/snesdev/65816-opcodes.html#rol-rotate-left
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#ROL
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.1.3