Freescale Semiconductor, Inc.
Operating Modes and On-Chip Memory
EPROM, EEPROM and CONFIG register
3.6.4 RAM and EEPROM security
The optional security feature protects the contents of EEPROM and
RAM from unauthorized access. A program, or a key portion of a
program, can be protected against duplication. To accomplish this, the
protection mechanism restricts operation of protected devices to single
chip modes, and thus prevents the memory locations from being
monitored externally (single chip modes do not allow visibility of the
internal address and data buses). Resident programs, however, have
unlimited access to the internal EEPROM and RAM and can read, write,
or transfer the contents of these memories. The NOSEC bit in the
CONFIG register disables this feature on devices that incorporate it.
Contact a Motorola representative for information on the availability of
this feature.
If the security feature is present and enabled and bootstrap mode is
selected, then the following sequence is performed by the bootstrap
program:
1. Output $FF on the SCI.
2. Turn block protect off. Clear BPROT register.
3. IF EEPROM is enabled, erase it all.
4. Verify that the EEPROM is erased; if not, begin sequence again.
5. Write $FF to every RAM byte.
6. Erase the CONFIG register.
If all the above operations are successful, the bootloading process
continues as if the device has not been secured.
CONFIG — System configuration register
State
Address bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
on reset
ROMA
D
NOSE NOCO ROMO
Configuration control (CONFIG) $003F
1
1
PAREN
EEON x11x 1xxx
C
P
N
For a description of the other bits contained in the CONFIG register refer
MC68HC11P2 — Rev 1.0
Technical Data
Operating Modes and On-Chip Memory
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