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ROR: Difference between revisions
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'''ROR''' (Rotate Right) is a 65x instruction that rotates a value and the [[carry flag]] right one bit. The least significant bit is shifted into the carry flag. The carry flag is shifted into the most significant bit. | '''ROR''' (Rotate Right) is a 65x instruction that rotates a value and the [[carry flag]] right one bit. The least significant bit is shifted into the carry flag. The carry flag is shifted into the most 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 | 6A | 1 byte | 2 cycles | ||||
| Absolute | 6E | 3 bytes | 6 cycles* | ||||
| Direct Page | 66 | 2 bytes | 5 cycles* | ||||
| Absolute Indexed by X | 7E | 3 bytes | 7 cycles* | ||||
| Direct Page Indexed by X | 76 | 2 bytes | 6 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| N | . | . | . | . | . | Z | C | |
ROR (Rotate Right) is a 65x instruction that rotates a value and the carry flag right one bit. The least significant bit is shifted into the carry flag. The carry flag is shifted into the most 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
ROR ROR A ROR addr ROR dp ROR addr, X ROR dp, X
Cycle Penalties
- Except in accumulator addressing, ROR takes two extra cycles when the accumulator is 16 bits wide.
- In direct page addressing modes, ROR takes another extra cycle if the low byte of the direct page register is nonzero.
ROR was originally broken and left out of the earliest 6502 datasheets before fixed.
See Also
External Links
- Eyes & Lichty page 491, on ROR: https://archive.org/details/0893037893ProgrammingThe65816/page/491
- lbid, page 191, before & after diagram on ROR: https://archive.org/details/0893037893ProgrammingThe65816/page/191
- Labiak page 175 on ROR: https://archive.org/details/Programming_the_65816/page/n185
- MCS6500 Manual page 150 on ROR: https://archive.org/details/mos_microcomputers_programming_manual/page/n171
- Carr page 269 on ROR: https://archive.org/details/6502UsersManual/page/n282
- Leventhal page 3-87 on ROR: https://archive.org/details/6502-assembly-language-programming/page/n136
- snes9x implementation of ROR: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1070
- undisbeliever on ROR: https://undisbeliever.net/snesdev/65816-opcodes.html#ror-rotate-right
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#ROR
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.1.3