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ST25DV04K Datasheet(PDF) 97 Page - STMicroelectronics |
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ST25DV04K Datasheet(HTML) 97 Page - STMicroelectronics |
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97 / 220 page  DocID027603 Rev 4 97/220 ST25DV04K ST25DV16K ST25DV64K I2C operation 219 6.6 I2C password management The ST25DVxxx controls I2C security session using an I2C 64-bit password. This I2C password is managed with two I2C dedicated commands: I2C present password and I2C write password. 6.6.1 I2C present password command description The I2C present password command is used in I2C mode to present the password to the ST25DVxxx. This is used to open I2C security session or to allow I2C password modification (see Section 5.6: Data Protection for detailed explanation about password usage). 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 30: I2C Present Password Sequence, 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 eight password data bytes, the validation code, 09h, 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 the 64-bit password twice to prevent any data corruption during the sequence. If the two 64-bit passwords sent are not exactly the same, the ST25DVxxx 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 ST25DVxxx compares the 64 received data bits with the 64 bits of the stored I2C password. If the values match, the I2C security session is open after the internal delay, and the I2C_SSO_Dyn register is set to 01h. If the values do not match, the I2C security session is closed and I2C_SSO_dyn register is set to 00h. During the internal delay, the serial data (SDA) signal is disabled internally, and the device does not respond to any requests. I2C_SSO_Dyn is a Dynamic register, it can be checked via I2C host to know If I2C security session is open. Figure 30. I2C Present Password Sequence |
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