Datasheet

45
32133D–11/2011
UC3D
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 8-2. 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 or aWire 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.
This fuse has no effect in devices with no External Memory
Interface (EBI).
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 or aWire chip erase.
BOOTPROT can only be changed when the security bit is
cleared.
If the security bit is set, only an external JTAG or aWire 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 8-4. Boot Loader Area Specified by BOOTPROT
BOOTPROT
Pages protected by
BOOTPROT
Size of protected
memory
7 None 0
6 0-1 512 byte
5 0-3 1Kbyte
4 0-7 2Kbyte
3 0-15 4Kbyte
2 0-31 8Kbyte
1 0-63 16Kbyte
0 0-127 32Kbyte