unit unCRC16_Modbus;

interface

function CalCRC16(AData:array of Byte; AStart,AEnd:Integer): Word;

implementation

function CalCRC16(AData:array of Byte; AStart,AEnd:Integer): Word;
const
  GENP = $A001;

var
  crc:Word;
  i:Integer;
  tmp:Byte;

procedure CalOneByte(AByte:Byte);
var
  j:Integer;
begin
  crc:=crc xor AByte;
  for j := 0 to 7 do
  begin
    tmp:=crc and 1;
    crc:=crc shr 1;
    crc:= crc and $7FFF;
    if tmp = 1 then
    crc:= crc xor GENP;
    crc:=crc and $FFFF;
  end;
end;

begin
  crc:=$FFFF;
  for i := AStart to AEnd do
  CalOneByte(AData【i】);
  Result:=crc;
end;

end.