ST8500 datasheet(14/37 Pages) STMICROELECTRONICS

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Device architecture

ST8500

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DocID031029 Rev 3

2.4.4

One Time Programmable (OTP) section

The ST8500 device embeds an OTP area that stores device sensitive information, security

control bits and additional user specific bytes. The OTP section has two different HW

protection methods, ECC or HW redundancy, as indicated in Table 4.

The ECC calculation unit improves robustness of data storage. This ECC block encodes

and decodes each 32-bits words in programming and reading operations. The user must

program all the ECC protected words in one shot, no modification is possible afterward.

The HW redundancy is a more flexible protection mechanism but limits the size of each

word to 16-bits. The user can write words in multiple shots but respecting this rule: the word

value can be changed only making '0's becoming '1's (in no case single bits can be written

back at 0).

Table 4. OTP section

Word

Word size

Protection

Description

016 bits

redundancy

User security bits:

b0: Cortex™-M4F images in clear text enabled

b1: Cortex™-M4F JTAG enabled

b2: user OTP write locked

b3: Cortex™-M4F key read locked

b4-15: reserved

32 bits

ECC

Cortex™-M4F image decryption key word0

32 bits

ECC

Cortex™-M4F image decryption key word1

32 bits

ECC

Cortex™-M4F image decryption key word2

32 bits

ECC

Cortex™-M4F image decryption key word3

32 bits

ECC

Cortex™-M4F image decryption key word4

32 bits

ECC

Cortex™-M4F image decryption key word5

32 bits

ECC

Cortex™-M4F image decryption key word6

32 bits

ECC

Cortex™-M4F image decryption key word7

32 bits

ECC

User specific word 0

32 bits

ECC

User specific word 1

32 bits

ECC

User specific word 2

32 bits

ECC

User specific word 3

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