Reading/programming the embedded Flash memory

PM0075

18/31

Doc ID 17863 Rev 2

●

All features linked to loading code into and executing code from the embedded SRAM

are still active (JTAG/SWD and boot from embedded SRAM) and this can be used to

disable the read protection. When the read protection option byte is altered to a

memory-unprotect value, a mass erase is performed.

●

When booting from the embedded SRAM, Flash memory accesses through the code

and through data read using DMA1 and DMA2 are not allowed.

●

Flash memory access through data read using JTAG, SWV (serial wire viewer), SWD

(serial wire debug), ETM and boundary scan are not allowed.

The Flash memory is protected when the RDP option byte and its complement contain the

pair of values shown in Table 6.

Note:

Erasing the option byte block will not trigger a mass erase as the erased value (0xFF)

corresponds to a protected value.

Unprotection

To disable the read protection from the embedded SRAM:

●

Erase the entire option byte area. As a result, the read protection code (RDP) will be

0xFF. At this stage the read protection is still enabled.

●

Program the correct RDP code 0x00A5 to unprotect the memory. This operation first

forces a Mass Erase of the main Flash memory.

●

Reset the device (POR Reset) to reload the option bytes (and the new RDP code) and,

to disable the read protection.

Note:

The read protection can be disabled using the boot loader (in this case only a System Reset

is necessary to reload the option bytes). For more details refer to AN2606.

2.4.2

Write protection

In high-density and connectivity line devices, from page 0 to page 61, write protection is

implemented with a granularity of two pages at a time. The remaining memory block (from

page 62 to page 255 in high-density devices, and from page 62 to page 127 in connectivity

line devices) is write-protected at once.

In low- and medium-density devices, write protection is implemented with a granularity of

four pages at a time.

If a program or an erase operation is performed on a protected page, the Flash memory

returns a protection error flag on the Flash memory Status Register (FLASH_SR).

The write protection is activated by configuring the WRP[3:0] option bytes, and then by

applying a system reset to reload the new WRPx option bytes.

Table 6.

Flash memory protection status

RDP byte value

RDP complement value

Read protection status

0xFF

0xFF

Protected

RDPRT

Complement of RDP byte

Not protected

Any value

Not the complement value of RDP

Protected