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

Operation

Y - 1 -> Y

Table

DEY | Decrement Index Register Y by 1
================================================

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

addressing       assembler    opc  bytes  cycles
------------------------------------------------
implied          DEY           88    1      2

Flags

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