Scan Clear (Zeroization)

Zynq UltraScale+ Device Technical Reference Manual (UG1085)

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2.4 English

Zeroization is a process in which zeros are shifted through all of the storage elements and then verified that the shift occurred correctly. This is achieved using the MBIST and scan clear functionality. The scan clear engines can only be controlled by the PMU and CSU processors through their direct interfaces to the engines. Other processors can request the PMU through the LOGCLR_TRIG register to start any specific scan clear engines.

Every power island and power domain have scan clear engines. The PMU and CSU blocks have separate scan clear engines even though they are not power islands. The PMU scan clear is triggered only on POR, and the CSU scan clear can only be triggered by the PMU. The LPD and FPD scan clear operations only run after a POR and during secure lockdown if the LPD_SC and FPD_SC eFUSE are programmed. The PMU scan clear is a mandatory security operation in the boot flow, whereas the LPD and FPD scan clear operations are optional. See Boot Flow for details on PMU security operations during boot flow.