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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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AM29PDL127H 데이터시트(PDF) 26 Page - Advanced Micro Devices |
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AM29PDL127H 데이터시트(HTML) 26 Page - Advanced Micro Devices |
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26 / 68 page  24 Am29PDL127H June 07, 2005 P RE L I M I NARY SECTOR PROTECTION The Am29PDL127H features several levels of sector protection, which can disable both the program and erase operations in certain sectors or sector groups: Persistent Sector Protection A command sector protection method that replaces the old 12 V controlled protection method. Password Sector Protection A highly sophisticated protection method that requires a password before changes to certain sectors or sec- tor groups are permitted WP# Hardware Protection A write protect pin that can prevent program or erase operations in sectors 0, 1, 268, and 269. The WP# Hardware Protection feature is always avail- able, independent of the software managed protection method chosen. Selecting a Sector Protection Mode All parts default to operate in the Persistent Sector Protection mode. The customer must then choose if the Persistent or Password Protection method is most desirable. There are two one-time programmable non-volatile bits that define which sector protection method will be used. If the Persistent Sector Protec- tion method is desired, programming the Persistent Sector Protection Mode Locking Bit permanently sets the device to the Persistent Sector Protection mode. If the Password Sector Protection method is de- sired, programming the Password Mode Locking Bit permanently sets the device to the Password Sector Protection mode. It is not possible to switch between the two protection modes once a locking bit has been set. One of the two modes must be selected when the device is first programmed. This prevents a pro- gram or virus from later setting the Password Mode Locking Bit, which would cause an unexpected shift from the default Persistent Sector Protection Mode into the Password Protection Mode. The device is shipped with all sectors unprotected. AMD offers the option of programming and protecting sectors at the factory prior to shipping the device through AMD’s ExpressFlash™ Service. Contact an AMD representative for details. It is possible to determine whether a sector is pro- tected or unprotected. See Autoselect Mode for de- tails. Persistent Sector Protection The Persistent Sector Protection method replaces the 12 V controlled protection method in previous AMD flash devices. This new method provides three differ- ent sector protection states: ■ Persistently Locked —The sector is protected and cannot be changed. ■ Dynamically Locked —The sector is protected and can be changed by a simple command. ■ Unlocked —The sector is unprotected and can be changed by a simple command. To achieve these states, three types of “bits” are used: Persistent Protection Bit (PPB) A single Persistent (non-volatile) Protection Bit is as- signed to a maximum four sectors (see the sector ad- dress tables for specific sector protection groupings). All 4 Kword boot-block sectors have individual sector Persistent Protection Bits (PPBs) for greater flexibility. Each PPB is individually modifiable through the PPB Write Command . The device erases all PPBs in parallel. If any PPB re- quires erasure, the device must be instructed to pre- program all of the sector PPBs prior to PPB erasure. Otherwise, a previously erased sector PPBs can po- tentially be over-erased. The flash device does not have a built-in means of preventing sector PPBs over-erasure . Persistent Protection Bit Lock (PPB Lock) The Persistent Protection Bit Lock (PPB Lock) is a glo- bal volatile bit. When set to “1”, the PPBs cannot be changed. When cleared (“0”), the PPBs are change- able. There is only one PPB Lock bit per device. The PPB Lock is cleared after power-up or hardware reset. There is no command sequence to unlock the PPB Lock. Dynamic Protection Bit (DYB) A volatile protection bit is assigned for each sector. After power-up or hardware reset, the contents of all DYBs is “0”. Each DYB is individually modifiable through the DYB Write Command. When the par ts are first shipped, the PPBs are cleared, the DYBs are cleared, and PPB Lock is de- faulted to power up in the cleared state – meaning the PPBs are changeable. When the device is first powered on the DYBs power up cleared (sectors not protected). The Protection State for each sector is determined by the logical OR of the PPB and the DYB related to that sector. For the sectors that have the PPBs cleared, the DYBs control whether or not the sector is protected or unprotected. By issuing the DYB Write command sequences, the DYBs will be set or cleared, thus placing each sector in the protected or unprotected state. These are the so-called Dynamic Locked or Unlocked states. They are called dynamic states because it is very easy to |
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