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ROL: Difference between revisions
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'''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. | '''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 8 bits wide, 9 bits are rotated. | ||
When the accumulator is 16 bits wide, 17 bits are rotated. | * When the accumulator is 16 bits wide, 17 bits are rotated. | ||
==== Syntax ==== | ==== Syntax ==== | ||
Revision as of 16:37, 4 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.
See Also
External Links
- Eyes & Lichty page 490, on ROL: https://archive.org/details/0893037893ProgrammingThe65816/page/490
- lbid page 190 before & after diagram of ROL: https://archive.org/details/0893037893ProgrammingThe65816/page/190
- Labiak page 174 on ROL: https://archive.org/details/Programming_the_65816/page/n184
- MCS6500 Manual page 149 on ROL: https://archive.org/details/mos_microcomputers_programming_manual/page/n170
- Carr page 269 on ROL: https://archive.org/details/6502UsersManual/page/n282
- Leventhal page 3-85 on ROL: https://archive.org/details/6502-assembly-language-programming/page/n134
- 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