M_DSR  equ $FFFFC9
M_DTXS equ $FFFFCD
M_DRXR equ $FFFFCB
M_STRQ equ 1
M_SRRQ equ 2
START equ $100
        org p:START

        clr a
READ
        brclr #M_SRRQ,x:M_DSR,WRITE
        movep x:M_DRXR,a
WRITE
        brclr #M_STRQ,x:M_DSR,READ
        movep a,x:M_DTXS
        add #1,a
        jmp READ