SAF-C164SM Infineon Technologies, SAF-C164SM Datasheet - Page 49

• Manufacturer Part Number: SAF-C164SM
• Description: 16-Bit CMOS Microcontroller
• Manufacturer: Infineon Technologies

3.5
The on-chip mask ROM of the C164CM can be protected against read accesses of both
code and data. ROM protection is established during the production process of the
device (a ROM mask can be ordered with a ROM protection or without it). No software
control is possible, i.e. the ROM protection cannot be disabled or enabled by software.
When a device has been produced with ROM protection active, the ROM contents are
protected against unauthorized access by the following measures:
• No data read accesses to the internal ROM are permitted by any instruction which is
• No codes fetches from the internal ROM can be made by any instruction which is
Note: ROM protection may be used for applications where the complete software fits into
User’s Manual
executed from any location outside the on-chip mask ROM (including IRAM, XRAM,
and external memory).
A program cannot read any data out of the protected ROM from outside.
The read data will be replaced by the default value 009B
location.
executed from any location outside the on-chip mask ROM (including IRAM, XRAM,
and external memory).
A program cannot branch to a location within the protected ROM from outside. This
applies to JUMPs as well as to RETurns. A called routine within RAM or external
memory can never return to the protected ROM.
The fetched code will be replaced by the default value 009B
location. This default value will be decoded as the instruction “TRAP #00” which will
restart program execution at location 00’0000
the on-chip ROM, or where the on-chip ROM holds initialization software which is
then replaced by external application software (for example). In the latter case no
data (constants, tables, etc.) can be stored within the ROM. The ROM itself should
be mapped to segment 1 before branching outside, so an interrupt vector table
can be established in external memory.
Protection of the On-Chip Mask ROM
3-11
H
.
H
for any read access to any
H
Memory Organization
for any access to any
C164CM/C164SM
Derivatives
V1.0, 2002-02