ϰ3.17
DATA  SEGMENT
      MESS  DB 'INPUP ERROR!'0AH0DH'$'
DATA  ENDS
CODE  SEGMENT
      ASSUME  DS:DATACS:CODE
START:MOV  AXDATA
      MOV  DSAX
      MOV  AH01H
      INT  21H
      CMP  AL'A'
      JB   ERR
      CMP  AL'Z'
      JA   ERR
      ADD  AL20H
      MOV  DLAL
      MOV  AH02H
      INT  21H
      JMP  EXIT
ERR:  MOV  DXOFFSET MESS
      MOV  AH09H
      INT  21H
EXIT: MOV  AH02H
      INT  21H
CODE  ENDS
      END  START
