04-21-2019, 03:55 AM
These two conversion routines were common in the early 80's when writing code in assembly language for the early 8-bit microprocessors. You might communicate via a serial port to peek and poke values in memory when debugging, so you needed a way to translate between an 8-bit value in memory and the ASCII representation of the value on the console.
These two routines are complementary. HEX2ASC takes an 8-bit value in X and returns the low and high ASCII representation of the value in X and Y. ASC2HEX does the opposite, taking two ASCII characters in X and Y and returning an 8-bit value in X. The two routines are listed separately but were entered together as can be seen in the line numbering.
Conditions:
HEX mode, word size 8 bits
Usage: HEX2ASC
Input:
X - 8 bit value
Output:
Y - ASCII character for upper nibble
X - ASCII character for lower nibble
Usage: ASC2HEX
Input:
Y - ASCII character for upper nibble
X - ASCII character for lower nibble
Output:
X - 8 bit value
Examples:
5Ch
GSB A
Y - 35h
X - 43h
x<>y
GSB B
X - C5h
Edit: Word size must be 8 bits due to Rotate-Left (RLn) instruction.
These two routines are complementary. HEX2ASC takes an 8-bit value in X and returns the low and high ASCII representation of the value in X and Y. ASC2HEX does the opposite, taking two ASCII characters in X and Y and returning an 8-bit value in X. The two routines are listed separately but were entered together as can be seen in the line numbering.
Conditions:
HEX mode, word size 8 bits
Usage: HEX2ASC
Input:
X - 8 bit value
Output:
Y - ASCII character for upper nibble
X - ASCII character for lower nibble
Code:
001 LBL A | 43 22 A HEX2ASC
002 STO 0 | 44 0
003 F | F
004 0 | 0
005 AND | 42 20 Mask high nibble
006 4 | 4
007 RLn | 42 E
008 GSB 0 | 21 0 Convert to ASCII
009 RCL 0 | 45 0
010 F | F Mask low nibble
011 AND | 42 20
012 GSB 0 | 21 0 Convert to ASCII
013 RTN | 43 21
014 LBL 0 | 43 22 0 Convert nibble to ASCII
015 A | A
016 x<=y | 43 1 Value A - F?
017 GTO 1 | 22 1 Yes
018 CLX | 43 35 Disable stack lift
019 3 | 3 ASCII "0"
020 0 | 0
021 + | 40 Add to value 0 - 9
022 RTN | 43 21
023 LBL 1 | 43 22 1 Nibble was A - F
024 CLX | 43 35 Disable stack lift
025 3 | 3 Offset to ASCII "A"
026 7 | 7
027 + | 40
028 RTN | 43 21Usage: ASC2HEX
Input:
Y - ASCII character for upper nibble
X - ASCII character for lower nibble
Output:
X - 8 bit value
Code:
029 LBL B | 43 22 B ASC2HEX
030 GSB 0 | 21 0 Convert low ASCII to nibble
031 x<>y | 34
032 GSB 0 | 21 0 Convert high ASCII to nibble
033 4 | 4
034 RLn | 42 E Shift result to high nibble
035 OR | 42 40 Combine nibbles to a byte result
036 RTN | 43 21
037 LBL 0 | 43 22 0 Convert ASCII to nibble 0 - F
038 STO 0 | 44 0
039 F | F
040 0 | 0
041 AND | 42 20 Mask upper ASCII
042 3 | 3
043 0 | 0
044 x=y | 43 49 Character "0" - "9"?
045 GTO 1 | 22 1 Yes
046 CLX | 43 35 Remove 30h from stack
047 Rv | 33
048 CLX | 43 35 Disable stack lift
049 RCL 0 | 45 0
050 F | F Low ASCII nibble
051 AND | 42 20
052 9 | 9 Convert to "A" - "F"
053 + | 40
054 RTN | 43 21
055 LBL 1 | 43 22 1 Character was "0" - "9"
056 CLX | 43 35 Remove 30h from stack
057 Rv | 33
058 CLX | 43 35 Disable stack lift
059 RCL 0 | 45 0
060 F | F
061 AND | 42 20
062 RTN | 43 21Examples:
5Ch
GSB A
Y - 35h
X - 43h
x<>y
GSB B
X - C5h
Edit: Word size must be 8 bits due to Rotate-Left (RLn) instruction.