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AM29DS323T70EI Datasheet(PDF) 20 Page - SPANSION |
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AM29DS323T70EI Datasheet(HTML) 20 Page - SPANSION |
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20 / 52 page  May 15, 2002 Am29DS32xG 19 ADV ANC E INFO RMAT ION SecSiTM (Secured Silicon) Sector Flash Memory Region The SecSi (Secured Silicon) Sector feature provides a 256-byte Flash memory region that enables perma- nent part identification through an Electronic Serial Number (ESN). The SecSi Sector uses a SecSi Sector Indicator Bit (DQ7) to indicate whether or not the SecSi Sector is locked when shipped from the factory. This bit is permanently set at the factory and cannot be changed, which prevents cloning of a factory locked part. This ensures the security of the ESN once the product is shipped to the field. AMD offers the device with the SecSi Sector either fac tor y lock ed or customer lock able. T he fac - tory-locked version is always protected when shipped from the factory, and has the SecSi (Secured Silicon) Sector Indicator Bit permanently set to a “1.” The cus- tomer-lockable version is shipped with the SecSi Sec- tor unprotected, allowing customers to utilize the that sector in any manner they choose. The customer-lock- able version has the SecSi (Secured Silicon) Sector Indicator Bit permanently set to a “0.” Thus, the SecSi Sector Indicator Bit prevents customer-lockable de- vices from being used to replace devices that are fac- tory locked. The system accesses the SecSi Sector through a command sequence (see “Enter SecSiTM Sector/Exit SecSi Sector Command Sequence”). After the system has written the Enter SecSi Sector command se- quence, it may read the SecSi Sector by using the ad- dresses normally occupied by the boot sectors. This mode of operation continues until the system issues the Exit SecSi Sector command sequence, or until power is removed from the device. On power-up, or following a hardware reset, the device reverts to send- ing commands to the boot sectors. Factory Locked: SecSi Sector Programmed and Protected At the Factory In a factory locked device, the SecSi Sector is pro- tected when the device is shipped from the factory. The SecSi Sector cannot be modified in any way. The device is available preprogrammed with one of the fol- lowing: ■ A random, secure ESN only ■ Customer code through the ExpressFlash service ■ Both a random, secure ESN and customer code through the ExpressFlash service. In devices that have an ESN, a Bottom Boot device w ill have the 1 6 -byte ESN at add r e sses 0 0000 0h–0 000 07h in w o r d m ode ( o r 000000h–00000Fh in byte mode). In the Top Boot de- vice t he ESN will be at add r e sses 1FF000h–1FF007Fh in word mode (or addresses 3FE000h–3FE0FFh in byte mode). Customers may opt to have their code programmed by AMD through the AMD ExpressFlash service. AMD programs the customer’s code, with or without the ran- dom ESN. The devices are then shipped from AMD’s factory with the SecSi Sector permanently locked. Contact an AMD representative for details on using AMD’s ExpressFlash service. Customer Lockable: SecSi Sector NOT Programmed or Protected At the Factory If the security feature is not required, the SecSi Sector can be treated as an additional 256-byte Flash mem- ory space, expanding the size of the available Flash array. Additionally, note the difference in the loca- tion of the ESN compared to previous Am29DL32x top boot factory locked devices. The SecSi Sector is one-time programmable, may not be erased, and can be locked only once. Note that the accelerated programming (ACC) and unlock bypass functions are not available when programming the SecSi Sector. The SecSi Sector area can be protected using one of the following procedures: ■ Write the three-cycle Enter SecSi Sector Region command sequence, and then follow the in-system sector protect algorithm as shown in Figure 2, ex- cept that RESET# may be at either V IH or VID. This allows in-system protection of the SecSi Sector without raising any device pin to a high voltage. Note that this method is only applicable to the SecSi Sector ■ Write the three-cycle Enter SecSi Sector Region command sequence, and then use the alternate method of sector protection described in the “Sec- tor/Sector Block Protection and Unprotection” sec- tion. The SecSi Sector is one-time programmable. Once the SecSi Sector is locked and verified, the system must write the Exit SecSi Sector Region command se- quence to return to reading and writing the remainder of the array. The SecSi Sector protection must be used with cau- tion since, once protected, there is no procedure avail- able for unprotecting the SecSi Sector area and none of the bits in the SecSi Sector memory space can be modified in any way. Hardware Data Protection The command sequence requirement of unlock cycles for programming or erasing provides data protection against inadvertent writes (refer to Table 14 for com- mand definitions). In addition, the following hardware data protection measures prevent accidental erasure or programming, which might otherwise be caused by spurious system level signals during V CC power-up and power-down transitions, or from system noise. |
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