Q. Show the Code Conversion with example?

The conversion of data from one form to another is required. Consequently we will discuss an illustration for converting a hexadecimal digit attained in ASCII form to binary form.

Program:

; This program converts an ASCII input to equivalent hex digit which it represents.

; So valid ASCII digits are 0 to 9, A to F and program presumes that the 

; ASCII digit is read from a location in memory known as ASCII. The hex result is 

; left in the AL. Because the program converts just one digit number the AL is 

; Sufficient for the results. Result in AL is made FF if character in ASCII 

; is not proper hex digit.

; ALGORITHM 

; IF number <30h THEN error

; ELSE

; IF number <3Ah THEN Subtract 30h (it's a number 0-9)

; ELSE (number is >39h)

; IF number <41h THEN error (number in range 3Ah-40h which is not a valid

; A-F character range)

; ELSE

; IF number <47h THEN Subtract 37h for letter A-F 41-46 (Please note 

; that 41h - 37h = Ah)

; ELSE ERROR

;

; PORTS: None used

; PROCEDURES: None

; REGISTERS: Uses CS, DS, AX,

;

DATA                         SEGMENT

ASCII DB 39h                       ; any experimental data

DATA ENDS

CODE SEGMENT

                                    ASSUME CS: CODE, DS: DATA

START:                       MOV AX, DATA ; initialise data segment

                                    MOV DS, AX  ; Register using AX

                                    MOV AL, ASCII ; Get the ASCII digits of the number

                                                                        ; start the conversion 

                                    CMP AL, 30h; If the ASCII digit is below 30h then it is not 

JB ERROR; a proper Hex digit

                                    CMP AL, 3Ah; compare it to 3Ah

                                    JB NUMBER; if greater then possibly a letter between A-F

                                    CMP AL, 41h; this step will be done if equal to or above 

; 3Ah

                                    JB ERROR; between 3Ah and 40h is error

                                    CMP AL, 46h

                                    JA ERROR; The ASCII is out of 0-9 and A-F range

                                    SUB AL, 37h; it's a letter in the range A-F so convert

                                    JMP CONVERTED

NUMBER:                  SUB AL, 30h; it is a number in the range 0-9 so convert

JMP CONVERTED

ERROR: MOV AL, 0FFh; you can also display some message here

CONVERTED: MOV AX, 4C00h

INT 21h; the hex result is in AL

CODE ENDS

END START