Function            Checksum_block - calculate checksum for a block

  Syntax              unsigned char Checksum_block(char *b, int size);

  Prototype in        comm.h

  Remarks             calculates a checksum value based on the block
                      given. A checksum value is commonly used by older
                      transmission protocols such as Xmodem.

  Return value        returns a checksum value for the block operated on.

  See also            CRC16_block(), CRC16tupdate(), CRC16update(),
                      CRC32tupdate()