通讯转换问题,救大侠们看看.

procedure TMain.Button7Click(Sender: TObject);
var
  chk: integer;
  sn:integer;
begin
  chk := 224 xor 8 xor sn xor 0 xor 0 xor 0 xor 0 xor 0;
  Comm1.WriteCommData(chr(224), Length(chr(224)));
  Comm1.WriteCommData(chr(8), Length(chr(8)));
  Comm1.WriteCommData(chr(sn), length(chr(sn)));
  Comm1.WriteCommData(char(0), Length(chr(0)));
  Comm1.WriteCommData(char(0), Length(chr(0)));
  Comm1.WriteCommData(char(0), Length(chr(0)));
  Comm1.WriteCommData(char(0), Length(chr(0)));
  Comm1.WriteCommData(chr(chk), Length(chr(chk)));
end;这段函数,当传入变量sn和chk的时候,提示char与pchar类型不符.
其他的则可以.请问是什么原因?