I'm looking at the user guide for the MSP430x5xx family. It says there in section 9.1 that:
The RCCTL0 register is protected with a key. Only if the correct key is written during a word write, the RCCTL0 register content can be modified. Byte write accesses or write accesses with a wrong key are ignored.
And in section 9.3.1 that:
Field RCKEY: RAM controller key. Always read as 69h. Must be written as 5Ah, otherwise the RAMCTL write is ignored.
Can anyone explain to me what a strange protection if the password (code) 5Ah is known? For what purpose it was made?
Why RCKEY always read as 69h (not 5Ah)?