LRC checksum in Delphi

I am trying to convert a C code to Delphi/pascal, but somehow I cannot get it to work, my approach was like this :

function CheckLRC(s : PChar) : Char;
var
  sum : char;
begin
  sum := #0;
  while (^s <> #0) do
  begin
    sum := (sum XOR ^s);
    inc (s)
  end;
  result := sum;
end;

Original C code was :

   Set LRC = 0
   For each byte b in the buffer
   do
     Set LRC = (LRC + b) AND 0xFF
   end do
   Set LRC = (((LRC XOR 0xFF) + 1) AND 0xFF)

Hope anyone out there is able to help me, and can confirm this is the correct way to do an LRC checksum ?

I guess the exact equivalence of this function may be:

function CheckLRC(const s: AnsiString): byte;
var i: integer;
begin
  result := 0;
  for i := 1 to length(s) do
    inc(result,ord(s[i]));
  result := (result xor $FF)+1; // or result := (not result)+1;
end;

All "and $FF" in original code is unneeded here, since we are using a byte as result.