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SEP: Difference between revisions
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'''SEP''' (Set Status Bits) is a [[65c816]] instruction that sets bits in the [[status register]] that correspond to set bits in the operand. | '''SEP''' (Set Status Bits) is a [[65c816]] instruction that sets bits in the [[status register]] that correspond to set bits in the operand. | ||
SEP is the only way to set the m and x flags directly (but [[PLP]] and [[RTI]] may set them too.)<sup>[1]</sup> But, SEP can't modify those two flags in [[emulation mode]] because they are being forced to be set. | SEP is the only way to set the m and x flags directly without disturbing the [[stack]] (but [[PLP]] and [[RTI]] may set them too.)<sup>[1]</sup> But, SEP can't modify those two flags in [[emulation mode]] because they are being forced to be set. | ||
==== Syntax ==== | ==== Syntax ==== | ||
Revision as of 17:07, 11 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Immediate | E2 | 2 bytes | 3 cycles | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| emulation mode | N | V | . | . | D | I | Z | C |
| native mode | N | V | M | X | D | I | Z | C |
SEP (Set Status Bits) is a 65c816 instruction that sets bits in the status register that correspond to set bits in the operand.
SEP is the only way to set the m and x flags directly without disturbing the stack (but PLP and RTI may set them too.)[1] But, SEP can't modify those two flags in emulation mode because they are being forced to be set.
Syntax
SEP #%nvmxdizc
If you only want to set one flag, SED, SEI, or SEC are smaller/faster than SEP.
See Also
References
- Eyes & Lichty, page 502 on SEP
- Labiak, page 183 on SEP
- snes9x implementation of SEP: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3203
- undisbeliever on SEP: https://undisbeliever.net/snesdev/65816-opcodes.html#sep-set-status-bits