1. A Hexadecimal Calculator
CALCUL.EXE
A Hexadecimal Calculator

2. mov ah,0eh ;3-
mov al,byte ptr hex_num+1 ;3-
int 10h ;3- To display the MSB of v1

3. db =
dw =
db 12h
db 34h
dw h
dw 9ah
dw bch

4. ASCII Code Table

5. Signed & unsigned numbers
binary
Decimal value
0111
0110
0101
0100
0011
0010
0001
0000
1111
1110
1101
1100
1011
1010
1001
1000 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
(-2^3, 2^2, 2^1, 2^0)

9. MOV AH,D ; D3H = Y
MOV CH,F ; F1H = Y
ADD AH,CH
MOV BH,6D ; 6DH = Y
SUB BH,CH
 AH = ? Y BH = ? Y

10. ASCII Code Table

11. ; ###################
; # Procedure name: hex_dig
; # Function: To detect if al contains the ASCII code of a legal hexadecimal digit
; # Exit: CF = 0 if al is an ASCII code between '0' and '9', 'A' and 'F', or 'a' and 'f'.
; # CF = 1 otherwise
; # Register Changed: Flags (changed by CMP)
hex_dig proc
cmp al,'0'
jb not_hex_dig
cmp al,'9'
jbe is_hex_dig
not_0_to_9:
cmp al,'A'
cmp al,'F'
not_A_to_F:
cmp al,'a'
cmp al,'f'
not_hex_dig:
stc
ret
is_hex_dig:
clc
hex_dig endp

12. ascii_to_hex proc cmp al,'0' jb not_hex_dig cmp al,'9' jbe is_0_to_9
; ###########################################
; # Procedure name: ascii_to_hex
; # Function: Convert an ASCII code (one byte) to hexadecimal number (one nibble plus a leading zero nibble)
; # Entry: AL = the ASCII-coded hexadecimal digit
; # Exit: AL = the hexadecimal nibble with leading zero nibble
; # CF = 0 if al is an ASCII code between '0' and '9', 'A' and 'F', or 'a' and 'f'.
; # CF = 1 otherwise
; # Register Changed: AL, Flags (changed by CMP)
; # Example: Entry:: AL = '8' = 38H Exit:: AL = 08H
ascii_to_hex proc
cmp al,'0'
jb not_hex_dig
cmp al,'9'
jbe is_0_to_9
not_0_to_9:
cmp al,'A'
cmp al,'F'
jbe is_A_to_F_big
not_A_to_F_big:
cmp al,'a'
cmp al,'f'
jbe is_a_to_f
not_hex_dig:
stc
ret
is_0_to_9:
sub al,'0'
jmp is_hex_dig
is_A_to_F_big:
sub al,'A'-10
is_a_to_f:
sub al,'a'-10
is_hex_dig:
clc
ascii_to_hex endp

13. ; ###########################################
; # Procedure name: ascii_2digit_to_hex_1byte
; # Function: Convert a 2-digit ASCII code (two bytes) to a 1-byte hexadecimal number
; # Entry: AH = the higher digit of two ASCII-coded hexadecimal digits
; # AL = the lower digit of two ASCII-coded hexadecimal digits
; # Exit: AL = the two digits of the hexadecimal number
; # Register Changed: AH, AL, Flags
; # Example: Entry AX = '6a'; Exit AL = 6ah.
ascii_2digit_to_hex_1byte proc
call ascii_to_hex ;4- Convert the lower digit of the ASCII-coded hexadecimal number to a hexadecimal nibble
rol ax,8 ;5- To exchange AH and AL.
call ascii_to_hex ;6- Convert the higher digit of the ASCII-coded hexadecimal number to a hexadecimal nibble
rol al,4 ;7- Move the left nibble to the right
or al,ah ;8- Combine the two nibble
ret
ascii_2digit_to_hex_1byte endp

14. ; ###########################################
; # Procedure name: hex_to_ascii
; # Function: Convert a hexadecimal number (one nibble plus a leading zero nibble) to an ASCII code (one byte)
; # Entry: AL = the hexadecimal nibble with leading zero nibble
; # Exit: AL = the ASCII-coded hexadecimal digit
; # Register Changed: AL, Flags (changed by CMP)
; # Example: Entry:: AL = 08H Exit: AL = '8' = 38H
; # Register changed: AL, Flags (changed by CMP or ADD)
hex_to_ascii proc
add al,30h
cmp al,3ah
jb below_a
add al,61h - 3ah
below_a: ret
hex_to_ascii endp

15. ; ###########################################
; # Procedure name: hex_1byte_to_ascii_2digit
; # Function: Convert a 1-byte hexadecimal number to a 2-digit ASCII code (two bytes)
; # Entry: AL = the two digits of the hexadecimal number
; # Exit: AH = the higher digit of two ASCII-coded hexadecimal digits
; # AL = the lower digit of two ASCII-coded hexadecimal digits
; # Register Changed: AH, AL, Flags
; # Example: Entry AL = 6ah; Exit AX = '6a'
hex_1byte_to_ascii_2digit proc
mov ah,al
and ah,0fh
shr al,4
call hex_to_ascii ;4- Convert the higher hexadecimal nibble to an ASCII-coded hexadecimal byte
rol ax,8 ;5- To exchange AH and AL.
call hex_to_ascii ;6- Convert the lower hexadecimal nibble to an ASCII-coded hexadecimal byte
ret
hex_1byte_to_ascii_2digit endp

16. mov hex_num,'00' ; To initialize hex_num get_1dig: mov ah,0eh ;3-
; ###########################################
; # Procedure name: get_hex_num_2dig
; # Function: Receive a 2-digit hexdecimal number from the keyboard
; # Exit: AX = the hexadecimal number
; # Note: '0' will lead user input
get_hex_num_2dig proc
pusha
mov hex_num,'00' ; To initialize hex_num
get_1dig:
mov ah,0eh ;3-
mov al,byte ptr hex_num+1 ;3-
int 10h ;3- To display the MSB of v1
mov al,byte ptr hex_num ;3-
int 10h ;3- To display the LSB of v1
mov ah,0 ;2-
int 16h ;2- To recieve a key from the keyboard
call hex_dig ;4- To distinguish hex and non-hex key
jc hex_num_in ;4- Any non-hex-dig key will be treated as an "Enter" key
mov ah,byte ptr hex_num ;7- New hex_num = LSB of old hex_num * 10H + entered digit
mov hex_num,ax ;7- To save the new hex_num
mov ah,0eh ;6-
mov al,bs ;6-
int 10h ;6- To go back one space
jmp get_1dig
hex_num dw '00'
hex_num_in:
popa
mov ax,hex_num
ret
get_hex_num_2dig endp

17. mov ah,0eh ;6-
mov al,bs ;6-
int 10h ;6- To go back one space
jmp get_1dig
hex_num dw '00'
hex_num_in:
popa
mov ax,hex_num
ret
get_hex_num_2dig endp