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BRA: Difference between revisions
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'''BRA''' (BRanch Always) is a [[65c816]] instruction that performs an unconditional jump. The signed displacement ranges from -128 to 127. The displacement is sign-extended to 16 bits and added to the [[program counter]]. | '''BRA''' (BRanch Always) is a [[65c816]] instruction that performs an unconditional jump. The signed displacement ranges from -128 to 127. The displacement is sign-extended to 16 bits and added to the [[program counter]]. The displacement is measured from the instruction following BRA. | ||
BRA is relocatable. No flags are affected. | BRA is relocatable. No flags are affected. | ||
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BRA nearlabel | BRA nearlabel | ||
</pre> | </pre> | ||
BRA has the same timing as other branches, it just has no "branch not taken" case. | |||
===== Cycle Penalty ===== | ===== Cycle Penalty ===== | ||
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=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/435 page 435] on BRA | ||
* [[Labiak]] | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n135 page 125] on BRA | ||
* snes9x implementation of BRA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1390 | * snes9x implementation of BRA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1390 | ||
* Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.2.1.1 | |||
[[Category:ASM]] | [[Category:ASM]] | ||
Latest revision as of 03:38, 8 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Program Counter Relative | 80 | 2 bytes | 3 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| . | . | . | . | . | . | . | . | |
BRA (BRanch Always) is a 65c816 instruction that performs an unconditional jump. The signed displacement ranges from -128 to 127. The displacement is sign-extended to 16 bits and added to the program counter. The displacement is measured from the instruction following BRA.
BRA is relocatable. No flags are affected.
Syntax
BRA nearlabel
BRA has the same timing as other branches, it just has no "branch not taken" case.
Cycle Penalty
- BRA takes one additional cycle if the branch crosses a page boundary in emulation mode.
See Also
External Links
- Eyes & Lichty, page 435 on BRA
- Labiak, page 125 on BRA
- snes9x implementation of BRA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1390
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.2.1.1