Feature: Memory
Permanent Lock, which is only available by application to Winbond – the instructions are not listed in the datasheet. For most users, a better option is the
Power Supply Lock-Down function. This has the same effect of locking the status register settings when the device is active, but each time the device is powered down the status register lock is lifted, leaving a window open to change the register settings every time the device is powered on before the Power Supply Lock-Down is implemented again.
Enhanced data protection As described here, there are several features of the operation of SpiFlash NOR Flash memories that may be used to protect critical data. These protection features help designers avoid the risk of their system being disabled by noise- caused bit errors, or a host SoC that has mistakenly overwritten critical data. The range of options for protecting
Table 2: The SEC register bit enables protection to be specified at sector level
asserted (WP = Low), no change to the BP and SEC settings can be made without pulling the WP pin high.
Ultimate protection Users of serial NOR Flash devices such as the Winbond SpiFlash series of products can guarantee that protected regions will never be programmed or erased after shipment from the factory – effectively turning protected blocks into one-time programmable (OTP) memory space. This is achieved by applying a permanent lock to the block and sector protection register settings. The so- called Active Permanent Lock can be applied with the SRL (Status Register Lock) register bit. This permanently, irrevocably locks the data in protected blocks. If a bug is found in protected code in future, or an important security update needs to be applied in the field, it cannot be done if the Active
Permanent Lock has been implemented. This is a serious consequence, and so Winbond requires a special instruction sequence to be followed to implement Active
data and locking the protection settings, is not necessarily well-known, even by long-standing users of NOR Flash memory devices. System designers can take advantage of these protection features to improve the reliability of their products’ field operation, simply by using the full array of register settings provided by Winbond in SpiFlash NOR Flash devices.
Figure 1: Pin assignments on the W25Q128JV SOIC package, showing the Write Protect (WP) pin
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