10.3.1

Lock Command

The Lock command is an irreversible sequence that will permanently prevent all future writing to the Security register.

Once the Lock command has been executed, the Security register becomes read-only.

Note:  Once the Security register has been locked, it cannot be unlocked.

The Lock command protocol emulates a byte write operation to the Security register. However, the A7 through A4 bits

of the word address must be set to 0110b (6h). The remaining bits of the word address and the data word are “don’t

care” bits. Even though these bits are “don’t cares”, they still must be transmitted to the part. An ACK response to the

word address and data word byte indicates the Security register is not currently locked. A NACK response indicates

the AT24CSW04X/AT24CSW08X is already locked. Refer to Determining the Lock State of the Security Register for

details about determining the Lock status of the AT24CSW04X/AT24CSW08X.

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 completion of that write cycle, subsequently making the Security

register permanently read-only. Read operations are always allowed to the device.

Figure 10-3. Lock Command

SCL

SDA

Device Address Byte

Word Address Byte

Data Word (Don’t Care bits)

Start

by

Host

ACK

from

Client

MSb

MSb

Stop

by

Host

MSb

1

2

3

4

5

6

7

8

9

1

0

1

1

#

0

0

1

2

3

4

5

6

7

8

9

X

X

X

X

X

X

X

X

0

0

1

1

0

X

X

X

X

0

1

2

3

4

5

6

7

8

9

ACK

from

Client

ACK

from

Client

Notes: 

1.

For the AT24CSW04X, the @ indicates the A1 address bit (see Table 6-3). For the AT24CSW08X, the @

indicates the A9 address bit.

2.

# indicates the hardware address value which is managed by the ordering code of the device (see Table 6-3

and Table 6-4).

10.3.2

Determining the Lock State of the Security Register

The Lock state of the device can be determined by sending a subset of the Lock command to the device. Only the

device address byte and word address byte need to be transmitted to the device to determine the Lock state. An ACK

response to the word address byte indicates the Lock has not been set while a NACK response indicates the Lock

has been set. If the Lock has already been set, it cannot be undone. The abbreviated Lock sequence is completed by

the host sending a Stop condition to the device.

Figure 10-4. Determining the Security Register Lock State

SCL

SDA

Device Address Byte

Word Address Byte

Start

by

Host

ACK

from

Client

MSb

MSb

1

2

3

4

5

6

7

8

9

1

0

1

1

0

0

1

2

3

4

5

6

7

8

9

0

1

1

0

X

X

X

X

0/1

ACK from Client

if Unlocked

NACK from Client

if Locked

Stop

by

Host

Notes: 

1.

For the AT24CSW04X, the @ indicates the A1 Address bit which is managed by the ordering code of the (see

Table 6-3). For the AT24CSW08X, the @ indicates the A9 address bit.

2.

# indicates the hardware address value which is managed by the ordering code of the device (see Table 6-3

and Table 6-4).

AT24CSW04X/AT24CSW08X

Security Register

and its subsidiaries

Datasheet

DS20006426B-page 31