60.6.5.1 BUSRAM4KB Erase Sequence

The BUSRAM4KB Erase sequence is activated by the clear signal. The Erase sequence processes 64-bit words and is necessary to degrade the BUSRAM4KB content as fast as possible.

BUSRAM4KB is erased only if its contents have been modified since the last erase, or if it is the first erase request since the backup reset was released. This mechanism prevents recurring erases that consume power unnecessarily, in particular when the backup area is powered only by the backup battery. See SECUMOD_SYSR for software management of the erase. Even if the physical erase of the memory is not done due to an empty memory, the intrusion flags are stored in the Status register.

The Erase automaton performs 64-bit accesses, allowing “as fast as possible” erase.

During the Erase sequence, the upper 1 Kbyte of memory (BUSRAM1KB) is still accessible by the system.

To enhance security, the Erase sequence fills the memory with random values.

The erase sequence takes 64 cycles of ICLK for a partial erase and 512 cycles of ICLK for a full erase.