M24LR64-R datasheet(27/128 Pages) STMICROELECTRONICS

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M24LR64-R

System memory area

Doc ID 15170 Rev 10

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4.5

M24LR64-R I2C password security

The M24LR64-R controls I2C sector write access using the 32-bit-long I2C password and

the 64-bit I2C_Write_Lock bit area. The I2C password value is managed using two I2C

commands: I2C Present Password and I2C Write Password.

4.5.1

I2C Present Password command description

The I2C Present Password command is used in I2C mode to present the password to the

M24LR64-R in order to modify the write access rights of all the memory sectors protected by

the I2C_Write_Lock bits, including the password itself. If the presented password is correct,

the access rights remain activated until the M24LR64-R is powered off or until a new I2C

Present Password command is issued.

Following a Start condition, the bus master sends a device select code with the Read/Write

bit (RW) reset to 0 and the Chip Enable bit E2 at 1. The device acknowledges this, as shown

in Figure 8, and waits for two I2C password address bytes 09h and 00h. The device

responds to each address byte with an acknowledge bit, and then waits for the 4 password

data bytes, the validation code, 09h, and a resend of the 4 password data bytes. The most

significant byte of the password is sent first, followed by the least significant bytes.

It is necessary to send the 32-bit password twice to prevent any data corruption during the

sequence. If the two 32-bit passwords sent are not exactly the same, the M24LR64-R does

not start the internal comparison.

When the bus master generates a Stop condition immediately after the Ack bit (during the

“10th bit” time slot), an internal delay equivalent to the write cycle time is triggered. A Stop

condition at any other time does not trigger the internal delay. During that delay, the

M24LR64-R compares the 32 received data bits with the 32 bits of the stored I2C password.

If the values match, the write access rights to all protected sectors are modified after the

internal delay. If the values do not match, the protected sectors remains protected.

During the internal delay, Serial Data (SDA) is disabled internally, and the device does not

respond to any requests.

Table 14.

System parameter sector

I2C byte address

Bits [31:24]

Bits [23:16]

Bits [15:8]

Bits [7:0]

E2 = 1

2304

I2C password (1)

Delivery state: I2C password= 0000 0000h, RF password = 0000 0000h,

E2 = 1

2308

RF password 1(1)

E2 = 1

2312

RF password 2(1)

E2 = 1

2316

RF password 3 (1)

E2 = 1

2320

DSFID (FFh)

AFI (00h)

ST reserved

E2 = 1

2324

UID

E2 = 1

2328

UID (E0h)

UID (02h)

UID

E2 = 1

2332

Mem_Size (03 07FFh)

IC Ref (2Ch)

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