Security - Motorola MC9S12C-Family User Manual

Device User Guide — 9S12C128DGV1/D V01.05
latched into these bits on the rising edge of the reset signal. The ROMCTL signal allows the setting of the
ROMON bit in the MISC register thus controlling whether the internal Flash is visible in the memory map.
ROMON = 1 mean the Flash is visible in the memory map. The state of the ROMCTL pin is latched into
the ROMON bit in the MISC register on the rising edge of the reset signal.
BKGD = PE6 =
MODC MODB
0 0
0 0
0 1
0 1
1 0
1 0
1 1
1 1
For further explanation on the modes refer to the S12_MEBI block guide.

4.3 Security

The device will make available a security feature preventing the unauthorized read and write of the
memory contents. This feature allows:
• Protection of the contents of FLASH,
• Operation in single-chip mode,
• Operation from external memory with internal FLASH disabled.
The user must be reminded that part of the security must lie with the user's code. An extreme example
would be user's code that dumps the contents of the internal program. This code would defeat the purpose
of security. At the same time the user may also wish to put a back door in the user's program. An example
66
Table 4-1 Mode Selection
PE5 = PP6 =
MODA ROMCTL
0 X
0
1
1
0 X
0
1
1
0 X
0
1
1
0 X
0
1
1
Table 4-2 Clock Selection Based on PE7
PE7 = XCLKS
1 Colpitts Oscillator selected
0 Pierce Oscillator/external clock selected
ROMON
Bit
Special Single Chip, BDM allowed and ACTIVE. BDM is
1 allowed in all other modes but a serial command is
required to make BDM active.
1
Emulation Expanded Narrow, BDM allowed
0
0 Special Test (Expanded Wide), BDM allowed
1
Emulation Expanded Wide, BDM allowed
0
1 Normal Single Chip, BDM allowed
0
Normal Expanded Narrow, BDM allowed
1
Peripheral; BDM allowed but bus operations would cause
1
bus conflicts (must not be used)
0
Normal Expanded Wide, BDM allowed
1
Description
Mode Description