11.3.1.1.1 Physical Sections

The Flash is physically divided into two fixed sections: A Read-While-Write (RWW) section and a No-Read-While-Write (NRWW) section.

The main differences between the two sections are as follows:
  • When erasing or writing a page located inside the RWW Flash, the NRWW Flash can be read during the operation
  • When erasing or writing a page located inside the NRWW Flash, the CPU is halted during the entire operation

The syntax “Read-While-Write section” refers to which section to program (erase or write) and not the one read. Only the code located inside the NRWW Flash is accessible by either executing a CPU instruction or reading data while the RWW Flash is being written or erased.

Note: The interrupt code located in the RWW section may halt the CPU if the associated interrupt is triggered while the NRWW section is erased or written. Disable the interrupt or place the interrupt code in the Boot Loader Code (BOOT) section to avoid this.

The figures and table below explain these two physical Flash sections in detail:

Figure 11-3. Read-While-Write Scenarios

Table 11-1. Read-While-Write Scenarios
Flash Section Erased/Written Flash Section Accessed CPU
RWW section NRWW section Running
NRWW section NRWW section Halted
RWW section RWW section Halted

Note:
  • The User Row is located in the RWW Flash. When erasing or writing a page in the User Row, the NRWW Flash can be read during the operation.
  • The physical section sizes are device-dependent. Refer to the Memory Overview section for further details.