//CP341读数据
FUNCTION FC485: VOID
VAR_TEMP
i : INT;
j : INT;
k : BOOL;
tempvalue1 : WORD;
tempvalue2 : WORD;
tempvalue3 : WORD;
END_VAR

//1.依据前6位功能码计算出CRC校验码的两个字节
tempvalue1 := 16#ffff;
FOR i:=0 TO 5 BY 1 DO
tempvalue1 := tempvalue1 XOR BYTE_TO_WORD(DB485.DBB[i]);
FOR j:=0 TO 7 BY 1 DO
tempvalue2 := tempvalue1;
tempvalue1 := SHR(IN := tempvalue1,N := 1);
tempvalue3 := tempvalue2 AND 16#0001;
k := (tempvalue3 <> 16#0000);
IF k=TRUE THEN
tempvalue1 := tempvalue1 XOR 16#A001;
END_IF;
END_FOR;
END_FOR;
DB485.DBB[6] := WORD_TO_BYTE ( tempvalue1 AND 16#00FF);
DB485.DBB[7] := WORD_TO_BYTE (SHR ( IN :=(tempvalue1 AND 16#FF00),N := 8));