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Accumulator: Difference between revisions
From SnesLab
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It can be freely transferred to/from both the [[X index register]] (see [[TAX]] and [[TXA]]) and the [[Y index register]] (see [[TAY]] and [[TYA]]) and also the stack (see [[PHA]] and [[PLA]]). | It can be freely transferred to/from both the [[X index register]] (see [[TAX]] and [[TXA]]) and the [[Y index register]] (see [[TAY]] and [[TYA]]) and also the stack (see [[PHA]] and [[PLA]]). | ||
It is not specified to have any particular value after reset. | |||
The [[S-SMP]]'s accumulator is always 8 bits wide. | The [[S-SMP]]'s accumulator is always 8 bits wide. | ||
Revision as of 15:39, 11 August 2024
An Accumulator is a very fast register inside a processor that acts as a mathematical scratch pad.
The 65c816's accumulator can be either 8 or 16 bits in size, as configured by the m flag. Labiak calls this 16-bit memory mode. When the direct page is coincident with the zero page, TDC is a good way to zero it.
The high byte ("B") is still retained even when the accumulator is 8 bits wide and can be accessed with XBA.
It can be freely transferred to/from both the X index register (see TAX and TXA) and the Y index register (see TAY and TYA) and also the stack (see PHA and PLA).
It is not specified to have any particular value after reset.
The S-SMP's accumulator is always 8 bits wide.
See Also
References
- Eyes & Lichty, page 27
- subparagraph 8.1.1 A Register on page 3-8-4 of Book II of the official Super Nintendo development manual