TC1784
System Control Unit (SCU)
User´s Manual
3-131
V1.1, 2011-05
32-bit SCU, V1.18
•
Sophisticated Password Access mechanism with fixed and user-definable password
fields
•
Access Error Detection: Invalid password (during first access) or invalid guard bits
(during second access) trigger the Watchdog reset generation
•
Overflow Error Detection: An overflow of the counter triggers the Watchdog reset
generation
•
Watchdog function can be disabled; access protection and ENDINIT bit monitor
function remain enabled
•
Double Reset Detection
3.8.3
The Endinit Function
It is a prerequisite to understand the ENDINIT bit and its function for better
understanding of the descriptions in the following sections. Hence, its function is
explained first.
There are a number of registers in the TC1784 that are usually programmed only once
during the initialization sequence of the application. Modification of such registers during
normal application run can have a severe impact on the overall operation of modules or
the entire system.
While the Supervisor Mode, that allows writes to registers only when it is active, provides
a certain level of protection against unintentional modifications, it may not provide
enough security for system-critical registers.
The TC1784 provides one more level of protection for such registers via the Endinit
feature. This is a highly secure write-protection scheme that makes unintentional
modifications of registers protected by this feature nearly impossible.
The Endinit feature consists of an ENDINIT bit incorporated in the WDT control register,
WDT_CON0. Registers protected via Endinit determine whether or not writes are
enabled. Writes are only enabled if bit ENDINIT = 0 AND Supervisor Mode is active.
Write attempts if this condition is not true will be discarded and the register contents will
not be modified in this case. The BCU controls the further operation following a
discarded write access.
To get the highest level of security, this bit is incorporated in the highly secure access
protection scheme implemented in the WDT. This is a complex procedure, that makes it
nearly impossible for the ENDINIT bit to be modified unintentionally. In addition, the WDT
monitors ENDINIT bit modifications by starting a time-out sequence each time software
opens access to the critical registers through clearing bit ENDINIT. If the time out period
ends before bit ENDINIT is set again, a malfunction of the software is assumed and a
reset request is generated.
The access-protection scheme and the Endinit time-out operation of the WDT is
described in the following sections.
lists the registers that are protected via
the Endinit feature in the TC1784.
Содержание TC1784
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