10.

Security Register

The AT24CSW01X/AT24CSW02X includes a 32-byte Security register. The Security register is segmented into a

16-byte read-only section and a 16-byte user-programmable section organized as 4 pages of 8 bytes each. The

user-programmable portion supports both byte write and page write operations. The read-only section contains a

pre-programmed ensured unique 128-bit serial number. The user-programmable portion may be permanently locked

at any time with the Lock command.

Table 10-1. Security Register Organization

Security Register Byte Number

0

1

...

14

15

16

17

...

30

31

Factory Programmed (Read-only)

0-15: Device Serial Number

User Programmable (Lockable)

10.1

Custom Programming Option

Microchip supports the preprogramming and subsequent locking of customer specific data in the user-programmable

portion of the Security register. Contact the local Microchip Sales representative for more details on this custom

solution.

10.2

Read Operations in the Security Register

Random read and sequential read operations are supported by the Security register provided the device address

uses a device type identifier of 1011b (Bh), and the A7 and A6 bits of the word address are set to 10b. Current

address reads in the Security register are not supported due to the fact that the required A7 and A6 address bits in

the word address byte do not get sent to the device.

The first 16 bytes of the Security register are by definition read-only and contain a preprogrammed ensured unique

128-bit serial number. The remaining 16 bytes of the Security register are user-programmable and can be locked

from any future programming operations (see Lock Command).

10.2.1

Address Pointer Behavior

The AT24CSW01X/AT24CSW02X contains a single Address Pointer that is shared between the EEPROM and the

Security register. As such, any read operation to the Security register should begin with a dummy write sequence (i.e.

random read) to ensure the Address Pointer is set to a known value. If the preceding operation was to the Security

register, the Address Pointer will retain the last access location incremented by one.

10.2.2

Serial Number Read

Reading the 128-bit serial number is similar to the sequential read sequence, but requires use of the device address

seen in a dummy write and a specific word address. The word address must begin with a 10b sequence regardless

of the intended address. If a word address other than 10b is used, the device will not output valid data.

Example: If the application desires to read the first byte of the serial number, the word address input would need to

be 80h.

Note:  The entire 128-bit value must be read from the starting address of the serial number block to ensure a unique

number. Reading the serial number from a location other than the first address of the block will not result in a unique

serial number.

When the end of the Security register is reached (32 bytes of data), the data word address will roll over to the

beginning of Security register starting with the most significant byte of the 128-bit serial number. The serial number

read operation or any read of the Security register is terminated when the host does not respond with an ACK and

instead issues a Stop condition.

AT24CSW01X/AT24CSW02X

Security Register

and its subsidiaries

Datasheet

DS20006396B-page 27