Atmel AT32UC3A3128, Manual

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137
32072H–AVR32–10/2012
AT32UC3A3
through a dedicated Peripheral Bus address. Some of the general-purpose fuse bits are
reserved for special purposes, and should not be used for other functions.:
The BOOTPROT fuses protects the following address space for the Boot Loader:
Table 12-2. General-purpose fuses with special functions
General-
Purpose fuse
number
Name Usage
15:0 LOCK Region lock bits.
16 EPFL
External Privileged Fetch Lock. Used to prevent the CPU from
fetching instructions from external memories when in privileged
mode. This bit can only be changed when the security bit is
cleared. The address range corresponding to external
memories is device-specific, and not known to the flash
controller. This fuse bit is simply routed out of the CPU or bus
system, the flash controller does not treat this fuse in any
special way, except that it can not be altered when the security
bit is set.
If the security bit is set, only an external JTAG Chip Erase can
clear EPFL. No internal commands can alter EPFL if the
security bit is set.
When the fuse is erased (i.e. "1"), the CPU can execute
instructions fetched from external memories. When the fuse is
programmed (i.e. "0"), instructions can not be executed from
external memories.
19:17 BOOTPROT
Used to select one of eight different bootloader sizes. Pages
included in the bootloader area can not be erased or
programmed except by a JTAG chip erase. BOOTPROT can
only be changed when the security bit is cleared.
If the security bit is set, only an external JTAG Chip Erase can
clear BOOTPROT, and thereby allow the pages protected by
BOOTPROT to be programmed. No internal commands can
alter BOOTPROT or the pages protected by BOOTPROT if the
security bit is set.
Table 12-3. Boot Loader area specified by BOOTPROT
BOOTPROT
Pages protected by
BOOTPROT Size of protected
memory
7 None 0
6 0-1 1kByte
5 0-3 2kByte
4 0-7 4kByte
3 0-15 8kByte
2 0-31 16kByte
1 0-63 32kByte
0 0-127 64kByte