24CS512-ESLASHP datasheet(33/66 Pages) MICROCHIP

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DS20005769C-page 33

24CS512

10.4

Locking the Security Register

The user-programmable portion of the Security register

can be permanently inhibited from future writing with

the lock operation. The status of the lock state can be

determined from the check lock operation.

10.4.1

LOCK OPERATION

The lock operation is an irreversible sequence that will

permanently prevent all future writing to the upper

128 bytes of the Security register. Once the lock oper-

ation has been executed, the entire 256-byte Security

The lock operation protocol emulates a byte write oper-

ation to the Security register, however, the A11 through

A8 bits of the word address must be set to ‘0110b’ (6h).

The remaining bits of the word address and the data

bytes are don’t care bits. Even though these bits are

don’t care bits, they still must be transmitted to the

device. If the remaining bits are not transmitted, this will

cause the write cycle to abort and the Security register

to remain unlocked.

ACK responses to the word address and data byte indi-

cate the Security register is not currently locked. NACK

response indicate the Security register region is

already locked.

Refer to Section 10.4.2 “Determining the Lock State

of the Security Register” for details about determining

the lock status of the Security register.

The sequence completes with a Stop condition being

sent to the device, which initiates a self-timed internal

write cycle. The lock operation will conclude upon com-

pletion of that write cycle, subsequently making the

Security register permanently read-only.

FIGURE 10-3:

SECURITY REGISTER LOCK OPERATION

Note:

Once the Security register has been

locked, it cannot be unlocked.

Note:

The lock operation cannot be inhibited by

asserting the Write-Protect pin. Refer to

Section 6.6 “Write Protection”, which

describes the device behavior with

respect to the Write-Protect pin status.

MSb

456

Device Address Byte

Word Address – Byte 0

A2 A1 A0

ACK

from

Client

ACK

from

Client

Start by

Host

MSb

123

Word Address – Byte 1

Data Byte

xx x

xx0

ACK

from

Client

ACK

from

Client

Stop by

Host

SCL

SDA

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