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 AT24CSW01x/AT24CS02x is already locked. Please refer to Determining the Lock State of the Security Register for details about determining the Lock status of the AT24CSW01x/AT24CS02x.

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

Note: # indicates the hardware address value which is managed by the ordering code of the device (see Table 6-2).