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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 ==== | ||
<pre> | <pre> | ||
SEP #nvmxdizc | SEP #%nvmxdizc | ||
</pre> | </pre> | ||
If you only want to set one flag, [[SED]], [[SEI]], or [[SEC]] are smaller/faster than SEP. Early 65c816 chips had a timing problem with SEP and [[REP]] which required a [[NOP]] to be inserted after them, or to stretch the clock.<sup>[5]</sup> | |||
=== See Also === | === See Also === | ||
* [[TSB]] | * [[TSB]] | ||
* [[Derailment]] | * [[Derailment]] | ||
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# snes9x implementation of SEP: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3203 | # 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 | # undisbeliever on SEP: https://undisbeliever.net/snesdev/65816-opcodes.html#sep-set-status-bits | ||
# http://forum.6502.org/viewtopic.php?f=4&t=5196 | |||
[[Category:ASM]] | [[Category:ASM]] | ||
Latest revision as of 20:37, 17 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. Early 65c816 chips had a timing problem with SEP and REP which required a NOP to be inserted after them, or to stretch the clock.[5]
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
- http://forum.6502.org/viewtopic.php?f=4&t=5196