.MODEL SMALL .STACK 100H .DATA PROMPT_1 DB \'Enter the Lower Case Letter : $\' PROMPT_2 DB \'The Upper Case Letter is : $\' .CODE MAIN PROC MOV AX, @DATA ; initialize DS MOV DS, AX LEA DX, PROMPT_1 ; load and print PROMPT_1 MOV AH, 9 INT 21H MOV AH, 1 ; read a letter INT 21H MOV BL, AL ; save the letter in BL MOV AH, 2 ; return carriage MOV DL, 0DH INT 21H MOV DL, 0AH ; line feed INT 21H LEA DX, PROMPT_2 ; load and print PROMPT_2 MOV AH, 9 INT 21H SUB BL, 20H ; convert a lower case letter to upper case letter MOV AH, 2 ; print the Upper case letter MOV DL, BL INT 21H MOV AH, 4CH ; return control to DOS INT 21H MAIN ENDP END MAIN