Atmel Evaluation Kit AT91SAM9X35-EK AT91SAM9X35-EK Data Sheet

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SAM9X35 [DATASHEET]

11055E–ATARM–10-Mar-2014

In order to bring security to the TWI, a write protection system has been implemented.

The write protection mode prevents the write of 

 and 

. When this mode is enabled and one of the protected registers is written, an error is generated in the 

 and the register write request is canceled. When a write protection error occurs the

WPROTERR flag is set and the address of the corresponding canceled register write is available in the WPROTADRR
field of the TWI_WPROT_STATUS register.

Due to the nature of the write protection feature, enabling and disabling the write protection mode requires the use of a
security code. Thus when enabling or disabling the write protection mode the SECURITY_CODE field of the 

 must be filled with the “TWI” ASCII code (0x545749) otherwise the register write will be

canceled.