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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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S29GL512N Fiches technique(PDF) 38 Page - Cypress Semiconductor |
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S29GL512N Fiches technique(HTML) 38 Page - Cypress Semiconductor |
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38 / 92 page  Document Number: 002-01522 Rev. *B Page 38 of 92 S29GL512N S29GL256N S29GL128N 7.15 Password Sector Protection The Password Sector Protection method allows an even higher level of security than the Persistent Sector Protection method. There are two main differences between the Persistent Sector Protection and the Password Sector Protection methods: When the device is first powered on, or comes out of a reset cycle, the PPB Lock Bit is set to the locked state, or the freeze state, rather than cleared to the unlocked state, or the unfreeze state. The only means to clear and unfreeze the PPB Lock Bit is by writing a unique 64-bit Password to the device. The Password Sector Protection method is otherwise identical to the Persistent Sector Protection method. A 64-bit password is the only additional tool utilized in this method. The password is stored in a one-time programmable (OTP) region outside of the flash memory. Once the Password Protection Mode Lock Bit is set, the password is permanently set with no means to read, program, or erase it. The password is used to clear and unfreeze the PPB Lock Bit. The Password Unlock command must be written to the flash, along with a password. The flash device internally compares the given password with the pre-programmed password. If they match, the PPB Lock Bit is cleared to the unfreezed state , and the PPB bits can be altered. If they do not match, the flash device does nothing. There is a built-in 2 µs delay for each password check after the valid 64-bit password is entered for the PPB Lock Bit to be cleared to the “unfreezed state”. This delay is intended to thwart any efforts to run a program that tries all possible combinations in order to crack the password. 7.16 Password and Password Protection Mode Lock Bit In order to select the Password Sector Protection method, the customer must first program the password. The factory recommends that the password be somehow correlated to the unique Electronic Serial Number (ESN) of the particular flash device. Each ESN is different for every flash device; therefore each password should be different for every flash device. While programming in the password region, the customer may perform Password Read operations. Once the desired password is programmed in, the customer must then set the Password Protection Mode Lock Bit. This operation achieves two objectives: 1. It permanently sets the device to operate using the Password Protection Mode. It is not possible to reverse this function. 2. It also disables all further commands to the password region. All program, and read operations are ignored. Both of these objectives are important, and if not carefully considered, may lead to unrecoverable errors. The user must be sure that the Password Sector Protection method is desired when programming the Password Protection Mode Lock Bit. More importantly, the user must be sure that the password is correct when the Password Protection Mode Lock Bit is programmed. Due to the fact that read operations are disabled, there is no means to read what the password is afterwards. If the password is lost after programming the Password Protection Mode Lock Bit, there is no way to clear and unfreeze the PPB Lock Bit. The Password Protection Mode Lock Bit, once programmed, prevents reading the 64-bit password on the DQ bus and further password programming. The Password Protection Mode Lock Bit is not erasable. Once Password Protection Mode Lock Bit is programmed, the Persistent Protection Mode Lock Bit is disabled from programming, guaranteeing that no changes to the protection scheme are allowed. 7.17 64-bit Password The 64-bit Password is located in its own memory space and is accessible through the use of the Password Program and Password Read commands. The password function works in conjunction with the Password Protection Mode Lock Bit, which when programmed, prevents the Password Read command from reading the contents of the password on the pins of the device. 7.18 Persistent Protection Bit Lock (PPB Lock Bit) A global volatile bit. The PPB Lock Bit is a volatile bit that reflects the state of the Password Protection Mode Lock Bit after power-up reset. If the Password Protection Mode Lock Bit is also programmed after programming the Password, the Password Unlock command must be issued to clear and unfreeze the PPB Lock Bit after a hardware reset (RESET# asserted) or a power-up reset. Successful execution of the Password Unlock command clears and unfreezes the PPB Lock Bit, allowing for sector PPB bits to be modified. Without issuing the Password Unlock command, while asserting RESET#, taking the device through a power-on reset, or issuing the PPB Lock Bit Set command sets the PPB Lock Bit to a the “freeze state”. If the Password Protection Mode Lock Bit is not programmed, the device defaults to Persistent Protection Mode. In the Persistent Protection Mode, the PPB Lock Bit is cleared to the unfreeze state after power-up or hardware reset. The PPB Lock Bit is set to the freeze state by issuing the PPB Lock Bit Set command. Once set to the freeze state the only means for clearing the PPB Lock Bit to |
Numéro de pièce similaire - S29GL512N |
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Description similaire - S29GL512N |
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