CRC校验，对16K_flash进行校验。举例：若校验码异常可以触发程序奔溃功能，达到程序加密效果。(// Program Descr iption:
//
// This program shows how to use the CRC engine in the automatic mode and the
// manual mode. The automatic mode can be used to calculate the CRC of flash
// pages. The manual mode can be used to calculate the CRC of any number of
// bytes manually written to the CRC engine.
//
// This program calculates the 16-bit CRC of the number of flash pages found in
// the global constant section. The first section uses the manual method to
// calculate the CRC of all bytes except the last two. The last two bytes
// store the resulting CRC value. The second section uses the automatic CRC
// feature to calculate the entire CRC, including the result stored in the last
// two bytes of the last flash pages. The final resulting CRC should be 0.
//
// NOTE: The block size of the CRC module is half the flash page size.
//　　　 The CRC block size is 256 bytes and the Flash page size is 512 bytes.)