MC9S12C Datasheet, PDF (59/680 Pages) Motorola, Inc – 16-Bit Microcontroller

Chapter 1 MC9S12C and MC9S12GC Device Overview (MC9S12C128)
BKGD = PE6 = PE5 =
MODC MODB MODA
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
PP6 =
ROMCTL
X
0
1
X
0
1
X
0
1
X
0
1
Table 1-7. Mode Selection
ROMON
Bit
Mode Description
Special Single Chip, BDM allowed and ACTIVE. BDM is allowed in
1
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
1
Peripheral; BDM allowed but bus operations would cause bus
conflicts (must not be used)
0
Normal Expanded Wide, BDM allowed
1
For further explanation on the modes refer to the S12_MEBI block guide.
Table 1-8. Clock Selection Based on PE7
PE7 = XCLKS
Description
1
Colpitts Oscillator selected
0
Pierce Oscillator/external clock selected
1.5.2 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
of this is the user downloads a key through the SCI which allows access to a programming routine that
updates parameters.
1.5.2.1 Securing the Microcontroller
Once the user has programmed the FLASH, the part can be secured by programming the security bits
located in the FLASH module. These non-volatile bits will keep the part secured through resetting the part
and through powering down the part.
Freescale Semiconductor
MC9S12C-Family / MC9S12GC-Family
59
Rev 01.23