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Index Register Select: Difference between revisions

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(started list of affected instructions)
Line 12: Line 12:
* [[PLP]]
* [[PLP]]
* [[RTI]]
* [[RTI]]
It affects the behavior of (incomplete list):
* [[LDX]]
* [[LDY]]
* [[STX]]
* [[STY]]
* [[TXY]]
* [[TYX]]


In [[emulation mode]], the x flag becomes the [[break flag]].
In [[emulation mode]], the x flag becomes the [[break flag]].

Revision as of 21:28, 9 August 2024

Index Register Select (X) is a flag in the processor status register (bit 4) of the 65c816. It indicates how wide the index registers are:

  • When clear, both index registers are 16 bits wide.
  • When set, both index registers are 8 bits wide.

It is not possible to control the width of the two index registers individually.

It can be affected by:

It affects the behavior of (incomplete list):

In emulation mode, the x flag becomes the break flag.

There are no BXS or BXC instructions that examine this flag.

See Also

Reference