3

        org 100h
Start:
        push TestStr
        call Proc

        mov ah, 09h
        mov dx, TestStr+1
        int 21h

        mov ah, 08h
        int 21h

Proc:
.prolog:
        push bp
        mov bp, sp
        sub sp, 0

.processing:
        mov di, [bp+4]
        movzx cx, byte[di]

.startLoop:
        inc di
        and byte[di], 1101'1111b
        loop .startLoop

.epilog:
        mov sp, bp
        pop bp
        ret 2

TestStr db 3, 'awa$'