function ConvertTo852(S: string): string;
var
  A : integer;
  Ch : char;
begin
  setlength(Result,Length(S));
  for A := 1 to length(S) do
  begin
    case S[A] of
      <code>: Ch := <852code>
      <code2>: Ch := <852code2>
      ...
      else Ch := S[A];
    end;
      Result[A] := Ch;
  end;
end;