ModBus RTU,CRC,数据转换代码

//======================================================================

function ModBusCRC(Data: string): string; //生成modbus CRC数据
var
  CRC16Lo, CRC16Hi, CL, CH, UseHi, UseLo: Dword;
  i, index: integer;
begin
  CRC16Lo := $FF; //CRC16Lo为CRC寄存器低8位
  CRC16Hi := $FF; //CRC16Hi为CRC寄存器高8位
  CL := $1;
  CH := $A0; // A001 H 是CRC－16多项式代码
  for i := 1 to Length(Data) do  begin
    CRC16Lo := CRC16Lo xor ord(Data[i]); //每一个数据与CRC寄存器异或
    for index := 0 to 7 do begin
      UseHi := CRC16Hi;
      UseLo := CRC16Lo;
      CRC16Hi := CRC16Hi shr 1;
      CRC16Lo := CRC16Lo shr 1; //右移一位
      if ((UseHi and $1) = $1) then //如果高位字节最后一位是1的话
        CRC16Lo := CRC16Lo or $80; //低位字节右移后前面补1

      if ((UseLo and $1) = $1) then begin//如果LSB 为1，则与多项式进行异或
        CRC16Hi := CRC16Hi xor CH;
        CRC16Lo := CRC16Lo xor CL;
      end;
    end;
  end;

  Result := Char(CRC16Lo) + Char(CRC16Hi);
end;

　　

function  ModBusDataToSingle(st: string; var Value: Single): Boolean;
var
  Pb: PByteArray;
begin
  Result := False;
  if Length(st) < 4 then
    Exit;
  Pb := PByteArray(@Value);
  Pb[3] := Ord(st[3]);
  Pb[2] := Ord(st[4]);
  Pb[1] := Ord(st[1]);
  Pb[0] := Ord(st[2]);
  Result := True;
end;

function  ModBusDataToWord(st: string; var Value: Word): Boolean;
begin
  Result := False;
  if Length(st) < 2 then
    Exit;
  Value := MakeWord(Ord(st[2]), Ord(st[1]));
  Result := True;
end;