We've just updated MediaWiki and its underlying software. If anything doesn't look or work quite right, please mention it to us. --RanAS
LSR: Difference between revisions
From SnesLab
(linkify admode) |
(added LSR image) |
||
| Line 60: | Line 60: | ||
* Except in [[accumulator addressing]], LSR takes an extra two cycles when the accumulator is 16 bits wide | * Except in [[accumulator addressing]], LSR takes an extra two cycles when the accumulator is 16 bits wide | ||
* In [[direct page addressing]] modes, LSR takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | * In [[direct page addressing]] modes, LSR takes another extra cycle if the low byte of the [[direct page register]] is nonzero. | ||
[[File:lsr.png]] | |||
=== See Also === | === See Also === | ||
Revision as of 18:17, 27 June 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Accumulator | 4A | 1 byte | 2 cycles | ||||
| Absolute | 4E | 3 bytes | 6 cycles* | ||||
| Direct Page | 46 | 2 bytes | 5 cycles* | ||||
| Absolute Indexed by X | 5E | 3 bytes | 7 cycles* | ||||
| Direct Page Indexed by X | 56 | 2 bytes | 6 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| 0 | . | . | . | . | . | |||
LSR (Logical Shift Right) is a 65x instruction that shifts a value one bit to the right (division by two). The most significant bit becomes a zero. The least significant bit is shifted into the carry flag.
Cycle Penalties
- Except in accumulator addressing, LSR takes an extra two cycles when the accumulator is 16 bits wide
- In direct page addressing modes, LSR takes another extra cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty page 465, on LSR: https://archive.org/details/0893037893ProgrammingThe65816/page/n491
- Labiak page 152 on LSR: https://archive.org/details/Programming_the_65816/page/n162
- MCS6500 Manual page 148 on LSR: https://archive.org/details/mos_microcomputers_programming_manual/page/n169
- Carr page 265 on LSR: https://archive.org/details/6502UsersManual/page/n278
- Leventhal page 3-76 on LSR: https://archive.org/details/6502-assembly-language-programming/page/n125
- snes9x implementation of LSR: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L862
- undisbeliever on LSR: https://undisbeliever.net/snesdev/65816-opcodes.html#lsr-logical-shift-right