mov al,[ecx]
cmp al,0x0
je done
cmp al,'a'
jb next
cmp al,'z'
ja next
sub al,0x20
mov [ecx],al
mov al,[ecx]
cmp al,0x0
je done
cmp al,' . ' ; добавил это
je done ; и это
cmp al,'a'
jb next
cmp al,'z'
ja next
sub al,0x20
mov [ecx],al