This device has dual-zone security for the Cortex-M3 subsystem. Because ZoneX (X → 1/2) software does not have access to program/data in ZoneY (Y → 2/1), code running from ZoneX cannot calculate CRC on data stored in ZoneY memory. Similarly, in the case of Exe-Only flash sectors, even though software is running from same secure zone, the software cannot read the data stored in Exe-Only sectors. However, hardware does allow CRC computation on data stored in Exe-Only flash sectors as long as the read access for this data is initiated by code running from same secure zone. These reads are just dummy reads and, in this case, read data only goes to the µCRC module, not to the CPU.