11.3.1.1.1 Physical Sections

The Flash is physically divided into two fixed sections, a Read-While-Write (RWW) section and a Non Read-While-Write (NRWW) section.

The main difference between the two sections are:
  • 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 is being programmed (erased or written) and not the one read. Only the code located inside the NRWW Flash can be accessed by either executing a CPU instruction or reading data while the RWW Flash is being written or erased.

Note: 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. Either disable the interrupt or place the interrupt code in the Boot Loader Code (BOOT) section to avoid this.

The figures and table below explain the two physical flash sections in more detail:

Figure 11-3. Read-While-Write Scenarios

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

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