Index Register Select

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:

• REP (might clear it)
• SEP (might set it)
• PLP
• RTI

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

See Also

• Memory/Accumulator Select

References

• Eyes & Lichty, page 422, Table 18.2. 65x Flags. https://archive.org/details/0893037893ProgrammingThe65816/page/422