Correct termiology for documentation

Answer 1

For a start, deliminator would probably be delimiter, although I notice your text has both delineator and deliminator in it - perhaps deliminator is a special delimiter/terminator combination :-)

However, a delimiter is usually used to separate fields and is usually present no matter what. What you have is an optional prefix which dictates the following field type. So I would probably call that a "prefix" or "type prefix" instead.

The "formatted string containing value expressions" I would just call a "value expression string" or "value string" to change it to a shorter form.

One other possible problem:

must be in the range -128 to 255 (inclusive) as they must fit in 8bytes

I think you mean 8 bits.

Answer 2

Try something like the following:

     ==== Value string encoding  ====
    The value string is at the core of the data used for low level
    transmissions.

    Within the value string the following refixes are used:
    # decimal
    $ Hex
    @ binary
    No prefix - ASCII.

    An optional sign may be included after the delimiter for negative numbers.
    Negative numbers are represented using twos complement.

    The value string may contain multiple values:
    eg: "a#21@1001111$-0F"

    All elements of the value string must represent an 8bit value and must
    be in the range -128 to 255

    When using ASCII representation the following characters that can't be sent
     * The delineator characters: $#@ (use prefixed hex value.)
     * Numbers written immediately after a value that could have
       contained those digits:
      * 0,1,2,3,4,5,6,7,8,9 for decimal
      * 0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,A,B,C,D,E,F for hex
      * 0,1 for binary