Motorola MC9S12GC-Family, MC9S12C-Family warranty Mode Selection

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.

Table 4-1 Mode Selection

BKGD =	PE6 =	PE5 =	PP6 =	ROMON	Mode Description
MODC	MODB	MODA	ROMCTL	Bit
					Special Single Chip, BDM allowed and ACTIVE. BDM is
0	0	0	X	1	allowed in all other modes but a serial command is
					required to make BDM active.
0	0	1	0	1	Emulation Expanded Narrow, BDM allowed
			1	0
0	1	0	X	0	Special Test (Expanded Wide), BDM allowed
0	1	1	0	1	Emulation Expanded Wide, BDM allowed
			1	0
1	0	0	X	1	Normal Single Chip, BDM allowed
1	0	1	0	0	Normal Expanded Narrow, BDM allowed
			1	1
1	1	0	X	1	Peripheral; BDM allowed but bus operations would cause
					bus conflicts (must not be used)
1	1	1	0	0	Normal Expanded Wide, BDM allowed
			1	1

For further explanation on the modes refer to the S12_MEBI block guide.

Table 4-2 Clock Selection Based on PE7

PE7 = XCLKS	Description
1	Colpitts Oscillator selected
0	Pierce Oscillator/external clock selected

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

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