MC68HC11PH8 Datasheet, PDF (76/264 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

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08/Apr/97@13:55 [DS97 v 4.1]
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PH8.DS03/Modes+mem
3.4.4 RAM and EEPROM security
The optional security feature protects the contents of EEPROM and RAM from unauthorized
access. Data, codes, keys, a program, or a key portion of a program, can be protected against
access. To accomplish this, the protection mechanism prevents operation of the device in special
test mode. Only resident programs have unlimited access to the internal EEPROM and RAM and
can read, write, or transfer the contents of these memories. To maintain RAM and EEPROM
security, the following conditions should be satisfied:
– The internal ROM must be enabled and mapped at $4000–$FFFF, by setting
the ROMON and ROMAD bits in the CONFIG register. This means that
program execution starts after reset under control of the internal ROM (See
Section 3.3.2.1).
– Access to external addresses should be restricted to data read or write.
Program execution should not point from the internal resources to the
external memory map.
– The FREEZ bit in the CONFIG register may be set to prevent internal
address visibility on the ports (See Section 3.3.2.1).
Alternatively, EEPROM-only security is possible:
– In expanded mode, program execution is possible in external resources, but
the EEPROM read or write access is restricted by internal hardware;
instructions must be executed from internal ROM/EPROM in the range
$4000 to $43FF (with ROMAD set) or in the range $0000 to $03FF (with
ROMAD clear). Avoid using indexed addressing in this ROM/EPROM range,
and clear temporary copies of EEPROM data before returning to the main
program.
– As above, the FREEZ bit in the CONFIG register may be set to prevent
internal address visibility on the ports (See Section 3.3.2.1).
Note:
A mask option on the MC68HC11PH8 determines whether or not the security feature
is available (it is always available on the MC68HC711PH8). If the feature is available,
then the secure mode can be invoked by programming the NOSEC bit to zero.
Otherwise, the NOSEC bit is permanently set to one, disabling security.
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MOTOROLA
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OPERATING MODES AND ON-CHIP MEMORY
¬^TPG
MC68HC11PH8