Someone

str2hex macro stringas
local @@10, @@loopas, @@kitascharas, @@done
  lea si, stringas
  call strlength
  mov cx, dx
  xor ax, ax
@@loopas:
  mov ax, [param3]
  mov bx, 0Ah
  mul bx
  mov param3, ax
  mov al, byte ptr[si]
  cmp al, 30h
  jb @@10
  cmp al, 40h
  jb @@20

  cmp al, 41h
  jb @@10
  cmp al, 48h
  jb @@30

  cmp al, 61h
  jb @@10
  cmp al, 67h
  ja @@10

  sub al, 61h
  add al, 0Ah
  jmp @@40
@@20:
  sub al, 30h
  jmp @@40
@@30:
  sub al, 41h
  add al, 0Ah
@@40:
  cbw
  add param3, ax
  inc si

  loop @@loopas
  jmp @@baigta
@@10:
  mov dx, offset error3_msg
  call write 
  jmp exit
@@baigta:
endm str2hex