Code:

function NumStringToBCD(const inStr: string): string;

function Pack(ch1, ch2: Char): Char;

begin

Assert((ch1 >= '0') and (ch1 <= '9'));

Assert((ch2 >= '0') and (ch2 <= '9'));

{Ord('0') is $30, so we can just use the low nybble of the character

as value.}

Result := Chr((Ord(ch1) and$F) or ((Ord(ch2) and$F) shl4))

end;

var

i: Integer;

begin

if Odd(Length(inStr)) then

Result := NumStringToBCD('0' + instr)

elsebegin

SetLength(Result, Length(inStr) div2);

for i := 1to Length(Result) do

Result[i] := Pack(inStr[2 * i - 1], inStr[2 * i]);

end;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

S1, S2: string;

begin

S1 := '15151515151515151515';

S2 := NumStringToBCD(S1);

memo1.lines.add('S1: ' + S1);

memo1.lines.add('Length(S2): ' + IntToStr(Length(S2)));

memo1.lines.add('S2 unpacked again: ' + BCDToNumString(S2));

end;