VMS Help RTL Routines, LIB$, LIB$CHAR, Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 one-character-string

    OpenVMS usage:char_string
    type:         character string
    access:       write only
    mechanism:    by descriptor

    ASCII character string consisting of a single character followed
    by trailing spaces, if needed, that LIB$CHAR creates when it
    transforms the ASCII character code. The one-character-string
    argument is the address of a descriptor pointing to the character
    string that LIB$CHAR writes.

 ascii-code

    OpenVMS usage:byte_unsigned
    type:         byte (unsigned)
    access:       read only
    mechanism:    by reference

    Single 8-bit ASCII character code that LIB$CHAR transforms to
    an ASCII string. The ascii-code argument is the address of an
    unsigned byte containing the ASCII character code.