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Memory/Accumulator Select: Difference between revisions
From SnesLab
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* When clear, the accumulator is 16 bits wide. It can only be clear in [[native mode]]. | * When clear, the accumulator is 16 bits wide. It can only be clear in [[native mode]]. | ||
* When set, the accumulator is 8 bits wide, but the high byte (B) is still retained. | * When set, the accumulator is 8 bits wide, but the high byte (B) is still retained. This is the case after reset because the processor is in [[emulation mode]]. | ||
It can be affected by: | It can be affected by: | ||
Revision as of 22:56, 9 August 2024
The Memory/Accumulator Select (M) flag exists in the processor status register (bit 5) of the 65c816. It indicates whether the accumulator is 8 or 16 bits wide:
- When clear, the accumulator is 16 bits wide. It can only be clear in native mode.
- When set, the accumulator is 8 bits wide, but the high byte (B) is still retained. This is the case after reset because the processor is in emulation mode.
It can be affected by:
It affects the behavior of (incomplete list):
But it does not affect XBA, TDC, or TCD.
There are no BMS or BMC instructions that examine this flag.
See Also
Reference
- Eyes & Lichty, page 422, Table 18.2. 65x Flags.