assume cs:codesg

datasg segment
    db "Beginner‘s All-purpose Symbolic Instruction Code.",0
datasg ends

codesg segment
begin:
    mov ax,datasg
    mov ds,ax
    mov si,0
    call letterc

    mov ax,4c00h
    int 21h

letterc:
    push cx
    mov ch,0
s0:
    mov cl,[si]
    jcxz ok 
    cmp cl,97
    jb s
    cmp cl,122
    ja s

    and cl,11011111b
    mov [si],cl
s:
    inc si
    jmp short s0 
ok:
    pop cx
    ret

codesg ends
end begin