ATECC508A datasheet(25/109 Pages) MICROCHIP

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Table 2-14. Data and OTP Zone Access Restrictions

Read Access

Write Access

LockValue == 0x55 (unlocked)

<Never>

Write

LockValue != 0x55 (locked)

Read

WriteNote

Note: After the data/OTP zones are locked using LockValue, reads and writes of the OTP zone

additionally depend on the state of the OTP mode bytes in the Configuration zone. See EEPROM One

Time Programmable (OTP) Zone for more information.

2.4.3

Individual Slot Locking

ATECC508A provides a mechanism for one-time locking of any of the 16 data slots. Once a slot is

individually locked, the slot can no longer be modified under any circumstances. This mechanism is

controlled by the 16-bit field SlotLocked in the configuration zone and the Lockable bit within each of the

16 KeyConfig words. The SlotLocked and lockable bits can be freely written using the Write command

prior to locking of the configuration zone.

•

SlotLocked Bits

If the SlotLocked bit for a particular slot is set to zero after the configuration zone is locked, then

modification of that slot via the PrivWrite, Write, GenKey, and/or DeriveKey commands is

permanently prohibited, regardless of the state of the corresponding Lockable, SlotConfig and/or

KeyConfig bits. When SlotLocked is zero, then the corresponding slot cannot be written even if the

data zone is unlocked.

•

Lockable Bits

After the configuration zone is locked, the state of the Lockable bit for a particular slot controls

whether or not the Lock command will be permitted to change the SlotLocked bit for the

corresponding slot, per the table below. If Lockable is one, then the Lock command can be used to

modify the SlotLocked bit either before or after the Data zone is locked.

Table 2-15. Individual Slot Locking After Configuration Zone is Locked

SlotLocked Bit Lockable Bit Lock Command PrivWrite, Write, DeriveKey,

and GenKey Commands

Notes

0 or 1

Not writeable.

Yes

Writeable but not lockable.

Yes

Writeable and lockable.

Individually lockable slots can contain either secret information or readable data and may be used in one

of two ways:

•

The Configuration zone and non-lockable data slots should be initialized and locked in the usual

manner by the OEM. After the data zone has been locked, those particular slots marked as

lockable can then be modified and individually locked in the field at some point in the future.

•

After the configuration zone is locked, some slots can be personalized and locked by the OEM prior

to transfer of the device/component to a second party such as a subcontractor or distributor that

personalizes the remaining slots, and then locks the data zone prior to shipment of the device into

the field.

The Lock command does not provide a CRC validation mechanism when using the individual slot locking

mechanism. If slots are locked prior to locking of the entire data zone, then the contents may be validated

ATECC508A

Device Organization

Datasheet Complete

DS20005927A-page 25

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