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BPL: Difference between revisions
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'''BPL''' (Branch if PLus) is a 65x instruction that performs a jump if the [[negative flag]] is clear. Note that zero is considered positive in the 65x architecture, so this instruction's behavior might be more accurately be described as "branch if non-negative." | '''BPL''' (Branch if PLus) is a 65x instruction that performs a jump if the [[negative flag]] is clear. Note that zero is considered positive in the 65x architecture, so this instruction's behavior might be more accurately be described as "branch if non-negative." | ||
The signed displacement of the target address can range from -128 to 127. | The signed displacement of the target address can range from -128 to 127. | ||
If the negative flag is set, control simply falls through to the instruction following BPL. | |||
No flags are affected. | |||
==== Syntax ==== | ==== Syntax ==== | ||
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</pre> | </pre> | ||
==== Cycle Penalties ==== | |||
* BPL takes one additional cycle if the branch is taken | * BPL takes one additional cycle if the branch is taken | ||
* BPL takes another extra cycle if that branch taken crosses a page boundary in [[emulation mode]]. | * BPL takes another extra cycle if that branch taken crosses a page boundary in [[emulation mode]]. | ||
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=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/434 page 434] on BPL | ||
* [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n134 page 124] on BPL | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n134 page 124] on BPL | ||
* [[MCS6500 Manual]] | * 4.1.2.2 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n55 page 40] on BPL | ||
* [[Carr]] | * [[Carr]], [https://archive.org/details/6502UsersManual/page/n264 page 251] on BPL | ||
* [[Leventhal]] | * [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n97 page 3-48] on BPL | ||
* snes9x implementation of BPL: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1385 | * snes9x implementation of BPL: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1385 | ||
Latest revision as of 22:39, 15 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Program Counter Relative | 10 | 2 bytes | 2 cycles* | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| . | . | . | . | . | . | . | . | |
BPL (Branch if PLus) is a 65x instruction that performs a jump if the negative flag is clear. Note that zero is considered positive in the 65x architecture, so this instruction's behavior might be more accurately be described as "branch if non-negative."
The signed displacement of the target address can range from -128 to 127.
If the negative flag is set, control simply falls through to the instruction following BPL.
No flags are affected.
Syntax
BPL nearlabel
Cycle Penalties
- BPL takes one additional cycle if the branch is taken
- BPL takes another extra cycle if that branch taken crosses a page boundary in emulation mode.
See Also
External Links
- Eyes & Lichty, page 434 on BPL
- Labiak, page 124 on BPL
- 4.1.2.2 on MCS6500 Manual, page 40 on BPL
- Carr, page 251 on BPL
- Leventhal, page 3-48 on BPL
- snes9x implementation of BPL: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1385