         result > 0xFF
 
     isSignedOverflow: (operand1, operand2, result) ->
-        @isBitSet (operand1 ^ result) & (operand2 ^ result), 7
+        not @isBitSet (operand1 ^ result) & (operand2 ^ result), 7
 
     ###########################################################
     # Operations table initialization

        status |= Bit1 if @zeroFlag
        status |= Bit2 if @interruptDisable
        status |= Bit3 if @decimalMode
        status |= Bit4 if @breakCommand
        status |= Bit6 if @overflowFlag
        status |= Bit7 if @negativeFlag
        status

        @tick()

    PLP: =>
        @setStatus @popByte()
        @tick()

    ###########################################################
