M24256E-F datasheet(8/46 Pages) STMICROELECTRONICS

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Bit b7:b4

Reserved bits - Read as '0'. (b7,b6,b5,b4)=(0,0,0,0)

Bit b3:b1

C2, C1, C0: Configurable device address bits

b3, b2, b1 are used to configure up to eight possibilities of chip enable address:

•

(b3, b2, b1) = (0, 0, 0): the chip enable address is 000 (factory delivery value)

•

(b3, b2, b1) = (0, 0, 1): the chip enable address is 001

•

(b3, b2, b1) = (0, 1, 0): the chip enable address is 010

•

(b3, b2, b1) = (0, 1, 1): the chip enable address is 011

•

(b3, b2, b1) = (1, 0, 0): the chip enable address is 100

•

(b3, b2, b1) = (1, 0, 1): the chip enable address is 101

•

(b3, b2, b1) = (1, 1 0): the chip enable address is 110

•

(b3, b2, b1) = (1, 1, 1): the chip enable address is 111

Bit b0

DAL: device address lock bit

b0 locks the CDA regster in read-only mode:

•

b0 = 0: bits b3,b2,b1,b0 can be modified

•

b0 = 1: bits b3,b2,b1,b0 cannot be modified and therefore the CDA register is frozen

Note: bits b3 to b0 can be updated (if b0 = 0) in the same write instruction. Setting b0 from 0 to 1 is an

irreversible action.

C2, C1, C0 and DAL are defining the chip enable address in the device select code and the device address lock.

These bits can be written and re-configured with a write command.

At power up or after reprogramming, the device load the last configuration of C2, C1, C0 and DAL values.

In order to prevent unwanted change of configurable device address bits, the M24256E proposes to protect the

CDA register,freezing it in read-only mode. The update of the CDA register is disabled (read-only) when the DAL

bit is set to '1' (DAL=1b).

In the same way, the update of the CDA register is enabled when the DAL bit is set to '0' (DAL= 0b).

Note:

•

Updating the DAL bit from 0 to 1 is an irreversible action: the C2,C1,C0 and DAL bits cannot be updated

any more.

•

If the write control input (WC) is driven high or if the DAL bit is set to 1, the write configurable device

address command is not executed and the accompanying data byte is not acknowledged, as shown in

Figure 7.

M24256E-F

Configurable device address register (CDA)

DS12687 - Rev 2

page 8/46

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