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LSR: Difference between revisions
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'''LSR''' (Logical Shift Right) is a 65x instruction that shifts a value one bit to the right (division by two). The most significant bit and [[negative flag]] are cleared. The least significant bit is shifted into the [[carry flag]]. | '''LSR''' (Logical Shift Right) is a 65x instruction that shifts a value one bit to the right (division by two). The most significant bit and [[negative flag]] are cleared. The least significant bit is shifted into the [[carry flag]]. | ||
==== Syntax ==== | |||
<pre> | |||
LSR A | |||
LSR addr | |||
LSR dp | |||
LSR addr, X | |||
LSR dp, X | |||
</pre> | |||
===== Cycle Penalties ===== | ===== Cycle Penalties ===== | ||
Revision as of 22:42, 6 July 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 and negative flag are cleared. The least significant bit is shifted into the carry flag.
Syntax
LSR A LSR addr LSR dp LSR addr, X LSR dp, X
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