ST25DV04K datasheet(98/220 Pages) STMICROELECTRONICS

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I2C operation

ST25DV04K ST25DV16K ST25DV64K

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DocID027603 Rev 4

6.6.2

I2C write password command description

The I2C write password command is used to update the I2C password value (register

I2C_PWD). It cannot be used to update any of the RF passwords. After the write cycle, the

new I2C password value is automatically activated. The I2C password value can only be

modified after issuing a valid I2C present password command.

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 31: I2C Write Password Sequence, and waits for the 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, 07h, and a resend of

the eight password data bytes. The most significant byte of the password is sent first,

followed by the least significant bytes.

It is necessary to send twice the 64-bit password to prevent any data corruption during the

write sequence. If the two 64-bit passwords sent are not exactly the same, the ST25DVxxx

does not modify the I2C password value.

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

tenth bit time slot), the internal write cycle is triggered. A Stop condition at any other time

does not trigger the internal write cycle.

During the internal write cycle, the serial data (SDA) signal is disabled internally, and the

device does not respond to any requests.

Caution:

I2C write password command data transits via the 256-Bytes fast transfer mode's buffer.

Consequently fast transfer mode must be deactivated before issuing a write password

command, otherwise command is NotACK (after address LSB), and programming is not

done and device goes in standby mode.

Figure 31. I2C Write Password Sequence

ST25DV04K Datasheet(PDF) 98 Page - STMicroelectronics