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DBNZ (SPC700): Difference between revisions
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'''DBNZ''' (Decrement Branch Non-Zero) is an [[SPC700]] instruction that decrements a [[direct page]] location or the [[Y index register]] and then jumps if that value is nonzero. The direct page index is the first operand and also the first byte immediately following the opcode. The relative branch offset is the second operand, the second byte following the opcode.<sup>[ | '''DBNZ''' (Decrement Branch Non-Zero) is an [[SPC700]] instruction that decrements a [[direct page]] location or the [[Y index register]] and then jumps if that value is nonzero. The direct page index is the first operand and also the first byte immediately following the opcode. The relative branch offset is the second operand, the second byte following the opcode.<sup>[3]</sup> | ||
No flags are affected. | No flags are affected. | ||
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DBNZ Y, rel | DBNZ Y, rel | ||
</pre> | </pre> | ||
Where rel is given in two's complement. | |||
=== See Also === | === See Also === | ||
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# Official Super Nintendo development manual on DBNZ: Table C-15, [https://archive.org/details/SNESDevManual/book1/page/n233 Appendix C-8 of Book I] | # Official Super Nintendo development manual on DBNZ: Table C-15, [https://archive.org/details/SNESDevManual/book1/page/n233 Appendix C-8 of Book I] | ||
# [https://www.romhacking.net/documents/197 anomie's SPC700 doc] | # [https://www.romhacking.net/documents/197 anomie's SPC700 doc] | ||
# lbid, https://github.com/yupferris/TasmShiz/blob/8fabc9764c33a7ae2520a76d80ed7220bb939f12/spc700.txt#L270 | |||
[[Category:ASM]] | [[Category:ASM]] | ||
[[Category:SPC700]] | [[Category:SPC700]] | ||
[[Category:Branching Commands]] | [[Category:Branching Commands]] | ||
Latest revision as of 19:33, 15 August 2024
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| Direct Page / Program Counter Relative | 6E | 3 bytes | when condition is false: 5 cycles
when condition is true: 7 cycles |
||||
| Implied (type 1) / Program Counter Relative | FE | 2 bytes | when condition is false: 4 cycles
when condition is true: 6 cycles | ||||
| Flags Affected | |||||||
|---|---|---|---|---|---|---|---|
| N | V | P | B | H | I | Z | C |
| . | . | . | . | . | . | . | . |
DBNZ (Decrement Branch Non-Zero) is an SPC700 instruction that decrements a direct page location or the Y index register and then jumps if that value is nonzero. The direct page index is the first operand and also the first byte immediately following the opcode. The relative branch offset is the second operand, the second byte following the opcode.[3]
No flags are affected.
Syntax
DBNZ dp, rel DBNZ Y, rel
Where rel is given in two's complement.
See Also
References
- Official Super Nintendo development manual on DBNZ: Table C-15, Appendix C-8 of Book I
- anomie's SPC700 doc
- lbid, https://github.com/yupferris/TasmShiz/blob/8fabc9764c33a7ae2520a76d80ed7220bb939f12/spc700.txt#L270