Flags Register
 
    The flags register contains various bits that control and record the
    state of the microprocessor, as defined below.
 
 
                Bit:    15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
                       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     Flags register:   |  |  |  |  |OF|DF|IF|TF|SF|ZF|  |AF|  |PF|  |CF|
                       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 
  ---------------------------------- Flags ----------------------------------
 
       Overflow            Set when an arithmetic overflow occurred.  An
                           arithmetic overflow occurs when the size of a
                           computation exceeds the size of the
                           destination.
 
       Direction           Set for auto-decrement with string
                           instructions, clear for auto-increment.
 
       Interrupt Enable    Interrupts are enabled as long as this flag is
                           set.  When this flag is cleared, interrupts
                           except for nonmaskable interrupts are disabled.
 
       Trap                This flag is used by debuggers to single step
                           through programs.  When this flag is set, an
                           INT 3 is generated after every instruction.
 
       Sign                Set when the high-order bit of the result is 1.
                           In other words, S = 0 for positive numbers and
                           S = 1 for negative numbers.
 
       Zero                Set whenever the result is 0.
 
       Auxiliary Carry     Set when the is a carry out of the lower half
                           of an 8 or 16 bit number, or when there is a
                           borrow from the upper to the lower half.  This
                           flag is used mainly by the decimal-arithmetic
                           instructions.
 
       Parity Flag         Set if there is an even number of 1-bits in the
                           result.  Cleared if there is an odd number of
                           1-bits.  Often used by communications programs
 
       Carry Flag          Set if there was a carry out of, or a borrow
                           into the high-order bit of the result.  This
                           flag is useful for propagating carries and
                           borrows for multi-word numbers.