     $A3/163:   Bit Counter Tape Read or Write
                Serial Bus EOI (End Of Input) Flag

      Used by Jiffy-DOS: LDFLG/QFLAG

       Used in all disk access and Load routines.

      Used by ByteBoiler: Temporary

    Kernal-Reference:

     BIT $A3     : $ED4C
     DEC $A3     : $FA00 $FC0E
     LDA $A3     : $F9C3 $FA18 $FC10
     LDX $A3     : $F969
     LSR $A3     : $ED1E
     ROR $A3     : $ED17
     STA $A3     : $FB99