.MODEL SMALL
.STACK 100H
.DATA
CR EQU 0DH
LF EQU 0AH

M1 DB CR,LF,' ENTER A HEXA DIGIT:$'
M2 DB CR,LF,'IN DECIMAL IT IS:'
C1 DB ?,'$'
M3 DB CR,LF,'DO YOU WANT TO DO IT AGAIN?'
DB 'Y/N','$'
M4 DB CR,LF,'ILLIGEL CHARACTER-ENTER'
DB '0..9OR A..F:','$'
M5 DB CR,LF,'IN DECIMAL IT IS:1'
C2 DB ?,'$'

.CODE
MAIN PROC
    MOV AX,@DATA
    MOV DS,AX

    BEGIN:  MOV AH,9
    LEA DX,M1
    INT 21H

    NEW:  MOV AH,1
    INT 21H

    CMP AL,'0'
    JL ILLEGAL
    CMP AL,'9'
    JG ILLEGAL

    MOV C1,AL
    MOV AH,9
    LEA DX,M2
    INT 21H

    MSG:  MOV AH,9
    LEA DX,M3
    INT 21H

    MOV AH,1
    INT 21H
    CMP AL,'Y'
    JE BEGIN
    CMP AL,'y'
    JE BEGIN
    JMP ENDD

    ILLEGAL:  CMP AL,'A'
    JL ILLEGAL2
    CMP AL,'F'
    JG ILLEGAL2
    SUB AL,11H
    MOV C2,AL

    MOV AH,9
    LEA DX,M5
    INT 21H

    JMP MSG

    ILLEGAL2:  MOV AH,9
    LEA DX,M4
    INT 21H
    JMP NEW

    ENDD:  MOV AH,4CH
    INT 21H

    MAIN ENDP
END MAIN