ATECC508A datasheet(23/109 Pages) MICROCHIP

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2.2.6

Special Memory Values in the Config Zone (Bytes 0 through 12)

Various fixed information is included in the ATECC508A that can never be written under any

circumstances and can always be read, regardless of the state of the lock bits.

•

SerialNum

Nine bytes (SN<0:8>) that together form a unique value that is never repeated for any device in the

CryptoAuthentication family. The serial number is divided into two groups:

–

SN<0:1> and SN<8>

The values of these bits are fixed at manufacturing time in most versions of the ATECC508A.

Their default value is 0x01 23 EE. These 24 bits are always included in the cryptographic

computations that the ATECC508A makes.

–

SN<2:3> and SN<4:7>

The values of these bits are programmed by Microchip during the manufacturing process and

are different for every die. These 48 bits are optionally included in some cryptographic

computations that are made by the ATECC508A.

•

RevNum

Four bytes of information that are used by Microchip to provide manufacturing revision information.

These bytes can be freely read as RevNum<0:3>, but they should never be used by system

software because they may be revised by Microchip occasionally.

2.3

EEPROM One Time Programmable (OTP) Zone

The OTP zone of 64 bytes (512 bits) is part of the EEPROM array, and can be used for read-only storage

or consumption logging purposes. It is organized as two blocks of 32 bytes each.

Prior to locking the Configuration zone (LockConfig=0x55), the OTP zone is inaccessible and can be

neither read nor written. After configuration locking, but prior to locking of the OTP zone (LockValue

=0x55), the entire OTP zone can be written using the Write command. If desired, the data to be written

can be encrypted. Prior to locking the data/OTP zones using LockValue, this zone cannot be read at all.

Once the OTP zone is locked, the OTPmode byte in the configuration zone controls the access

permissions of this zone as follows:

•

Read-only Mode

The data cannot be modified and would be used to store fixed model numbers, calibration

information, manufacturing history, or other data that should never change. The Write command

will always return an error and leave the memory unmodified.

All 64 bytes within the OTP zone are always available for reading using either 4 or 32 byte reads.

•

Consumption Mode

The bits function as one-way fuses and can be used to track consumption or usage of the item to

which the ATECC508A device is attached. In a battery, for example, they might be used to track

charging cycles or use time. In a printer ink cartridge, they might track the quantity of material

consumed. In a medical device, they might track the number of permitted uses for a limited use

item.

The Write command can only cause bits to transition from a one to a zero. Logically, this means

that the data value in the input parameter list will be ANDed with the current value in the word(s),

and the result written back to memory. As an example, writing a value of 0xFF results in no change

to the byte and writing a value of 0x00 causes the byte in memory to go to zero, regardless of the

previous value. Once a bit has transitioned to a zero, it can never transition back to a one.

All 64 bytes within the OTP zone are always available for reading using either 4 or 32 byte reads.

ATECC508A

Device Organization

Datasheet Complete

DS20005927A-page 23

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