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X Index Register: Difference between revisions
From SnesLab
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Unlike the [[Y index register]], the value of the [[stack pointer]] can be transferred to/from X with [[TXS]] and [[TSX]]. | Unlike the [[Y index register]], the value of the [[stack pointer]] can be transferred to/from X with [[TXS]] and [[TSX]]. | ||
It is not specified to have any particular value after reset. | |||
=== See Also === | === See Also === | ||
Revision as of 15:39, 11 August 2024
The X Index Register on 65x processors often holds the current index when iterating over things. It can be incremented or decremented by one with INX or DEX, but there is no instruction to add or subtract more than one.
On the S-SMP it is always 8 bits wide. It is the divisor for division commands.[2]
On the 65c816, it may be 8 or 16 bits wide. Indexing may cross bank boundaries.[1]
Unlike the Y index register, the value of the stack pointer can be transferred to/from X with TXS and TSX.
It is not specified to have any particular value after reset.
See Also
References
- https://wilsonminesco.com/816myths
- 8.1.2 of page 3-8-4 of Book I of the official Super Nintendo development manual