//GET THE SYSTEM CLOCK

      CALL  "READ_CLK"

       RET_VAL:=#STATUS1

       CDT    :=#SYSTEM_DATE_AND_TIME

//MOVE SYSTEM CLOCK INFO INTO DB499

      CALL  "Block Move"

       SRCBLK :=#SYSTEM_DATE_AND_TIME

       RET_VAL:=#STATUS1

       DSTBLK :="DATE AND TIME BCD".TimeStamp

//CONVERT YEAR VALUE FROM BCD TO INTEGER AND CONVERT TO ACTUAL YEAR

      L     "DATE AND TIME BCD".TimeStamp.Year

      BTI   

      T     "DATE AND TIME INT".DateYear

      L     2000

      +I    

      T     "DATE AND TIME INT".YearActual

//CONVERT MONTH VALUE FROM BCD TO INTEGER

      L     "DATE AND TIME BCD".TimeStamp.Month

      BTI   

      T     "DATE AND TIME INT".DateMonth

//CONVERT DAY VALUE FROM BCD TO INTEGER

      L     "DATE AND TIME BCD".TimeStamp.Day

      BTI   

      T     "DATE AND TIME INT".DateDay

//CONVERT HOUR VALUE FROM BCD TO INTEGER

      L     "DATE AND TIME BCD".TimeStamp.Hour

      BTI   

      T     "DATE AND TIME INT".DateHour

//CONVERT MINUTE VALUE FROM BCD TO INTEGER

      L     "DATE AND TIME BCD".TimeStamp.Minute

      BTI   

      T     "DATE AND TIME INT".DateMinute

//CONVERT SECOND VALUE FROM BCD TO INTEGER

      L     "DATE AND TIME BCD".TimeStamp.Second

      BTI   

      T     "DATE AND TIME INT".DateSecond

帮忙注释一下这段S7-300西门子PLC程序，谢谢！