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Half-Carry Flag: Difference between revisions
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The '''Half-carry flag''' (H) is bit 3 of the [[S-SMP]]'s [[program status word]]. It applies to the bottom 4 bits of the accumulator, meaning it is set whenever bit 3 of an [[ALU]] operation carries over into bit 4. It is also set when there has not been any borrow. | The '''Half-carry flag''' (H) is bit 3 of the [[S-SMP]]'s [[program status word]]. It applies to the bottom 4 bits of the [[accumulator]], meaning it is set whenever bit 3 of an [[ALU]] operation carries over into bit 4. It is also set when there has not been any borrow. | ||
It is cleared by [[CLRV]], but there is no [[SETV]] command to set it. | It is cleared by [[CLRV]], but there is no [[SETV]] command to set it. | ||
Revision as of 22:01, 14 August 2024
The Half-carry flag (H) is bit 3 of the S-SMP's program status word. It applies to the bottom 4 bits of the accumulator, meaning it is set whenever bit 3 of an ALU operation carries over into bit 4. It is also set when there has not been any borrow.
It is cleared by CLRV, but there is no SETV command to set it.
Whenever H is set, the overflow flag is set as well.
Both DAA and DAS examine the half-carry flag.
See Also
References
- https://problemkaputt.de/fullsnes.htm#snesapuspc700cpuoverview
- Page 3-8-6 of Book I of the official Super Nintendo development manual