void CRC1(unsigned char b) {
  b ^= CRCLo;
  CRCLo = CRCHi;
  CRCHi = b ^ (b << 4);
  CRCLo ^= (CRCHi >> 4) ^ (CRCHi << 3);
  CRCHi ^= (CRCHi >> 5);
}