M24LR04E-R datasheet(39/142 Pages) STMICROELECTRONICS

39 / 142 page

M24LR04E-R

I2C device operation

Doc ID 022208 Rev 5

39/142

5.16

M24LR04E-R I2C password security

The M24LR04E-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.

5.16.1

I2C present password command description

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

M24LR04E-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 M24LR04E-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 12, 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 four

password data bytes, the validation code, 09h, and a resend of the four 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 M24LR04E-R does

not start the internal comparison.

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

tenth 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

M24LR04E-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, the serial data (SDA) signal is disabled internally, and the device

does not respond to any requests.

Figure 12.

I2C present password command

ai15125c

Device select

code

Password

address 09h

Password

address 00h

Password

[31:24]

Ack

R/W

Ack

Device select code = 1010 1 1 1

Password

[23:16]

Password

[15:8]

Password

[7:0]

Ack

Ack generated during 9th bit time slot.

Validation

code 09h

Ack

Password

[31:24]

Ack

Password

[23:16]

Password

[15:8]

Password

[7:0]

Ack

M24LR04E-R 数据表(PDF) 39 Page - STMicroelectronics

M24LR04E-R 数据表(HTML) 39 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载

链接网址

M24LR04E-R 数据表(PDF) 39 Page - STMicroelectronics

M24LR04E-R 数据表(HTML) 39 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表 下载

链接网址

数据表下载