UM0116

Flash memory protection

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3.4.3

Flash NV access protection register 1 (FLASH_NVAPR1)

Address offset: 0x10 DFBC

Delivery value: 0xFFFF FFFF

The FLASH_NVAPR1 register is organized as 16 pairs of bits (PENx - PDSx). The delivery

value of The FLASH_NVAPR1 register is 0xFFFFFFFF. The first time you disable the

DEBUG/READOUT protection you must program to PDS0 ‘0’. To re-enable the protection

you must program to bit PEN0 ‘0’: this is possible only if PDS0 has been already

programmed to ‘0’. This cycle of disabling/re-enabling the protection can be repeated with

the next PDS1/PEN1 pair of bits and so on. PDS1 can be programmed to ‘0’ only if PEN0

has been already programmed to ‘0’, PEN1 can be programmed to ‘0’ if and only if PDS1

has been already programmed to ‘0’. The programming to ‘0’ of the bits of the

FLASH_NVAPR1 register must therefore follow the PDS0-PEN0-PDS1-PEN1-PDS2-PEN2-

...-PEN15 sequence, obtaining up to 16 unprotection/protection cycles.

Note:

At any reset event the non-volatile part of FLASH_NVAPR1 register is copied into its volatile

part. Unlike with the FLASH_NVAPR0 and FLASH_NVWPAR register, any write will always

update both the volatile and the non-volatile parts: i.e. no temporary unprotection is possible

with FLASH_NVAPR1 register.

Note:

All the STR73x Flash protection registers (FLASH_NVWPAR, FLASH_NVAPR0 and

FLASH_NVAPR1) are write only in User boot modes and Read/Write when booting from

SystemMemory mode.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

PEN[15:0]

rw

15

14

13

12

11

10

9

8

7

65432

1

0

PDS[15:0]

rw

Bit 31:16

PEN15-0: Protection Enable 15-0.

If bit PENx is programmed at 0 and bit PDSx+1 is erased to 1, the action of

bit DEBUG is enabled again. Bit PENx can be programmed to 0 only if bit

PDSx has been already programmed to 0.

Bit 15:0

PDS15-0: Protection Disable 15-0.

If bit PDSx is programmed at 0 and bit PENx is erased to 1, the action of bit

DEBUG is disabled (i.e. DEBUG/READOUT protection is no longer in place).

Bit PDS0 can be programmed at 0 only if bit DEBUG is already programmed

at 0. Bit PDSx can be programmed to 0 only if bit PENx-1 has already been

programmed to 0.