STI              Set Interrupt Enable Flag           Flags: O D I T S Z A P C
                                                                1
          Logic:    IF . 1

    STI sets the Interrupt Enable Flag, permitting the processor to
    recognize maskable interrupts. No other flags are affected. (Non-
    maskable interrupts are recognized no matter what the state of the
    interrupt enable flag.)

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   Operands                  Clocks   Transfers  Bytes   Example
   no operands                 2          -        1     STI
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       Notes:         A pending interrupt will not be recognized until
                      after the instruction following the STI executes.