½ is not a character in the ASCII character set.
The values you’re finding online probably differ because they’re using different character sets. For example, before Unicode was invented, localized versions of Windows all used different code pages, in which the basic ASCII set was extended with some additional characters.
Now, of course, everything is (or should be) fully Unicode. Detailed Unicode information for that character (vulgar fraction one half) can be found here. Note that there are also multiple representations for the same numerical value (e.g., base 10, hex, binary, etc.).
In Windows if you use the ALT codes,
3 digits will insert the equivalent “Code page 850” character
so ALT + 171 will insert the ½ symbol
189 is the ANSI/UTF-8/WIN-1252/ISO8859-1 value for the ½ symbol.
To use ALT codes for ANSI you MUST press 0 first,
so ALT + 0189 inserts the ½ symbol