Subtract 1, in two's complement, from the X register

Operation

X - 1 -> X

Table

DEX | Decrement Index Register X by 1
================================================

X - 1 -> X                       N V - B D I Z C
                                 + - - - - - + -

addressing       assembler    opc  bytes  cycles
------------------------------------------------
implied          DEX           CA    1     2

Flags

• Negative: 1 if bit 7 of result is 1; 0 otherwise
• Zero: 1 if result is zero; 0 otherwise