
Clock Functions
Limp-Home and Fast STOP Recovery modes
MC68HC912DG128 — Rev 3.0
Technical Data
MOTOROLA
Clock Functions
177
LHIE — Limp-Home Interrupt Enable
0 = Limp-Home interrupt is disabled
1 = Limp-Home interrupt is enabled
Forced to 0 when VDDPLL is at VSS level.
NOLHM —No Limp-Home Mode
0 = Loss of reference clock forces the MCU in limp-home mode.
1 = Loss of reference clock causes standard Clock Monitor reset.
Read anytime; Normal modes: write once; Special modes: write
anytime. Forced to 1 when VDDPLL is at VSS level.
Read and write anytime. Exceptions are listed below for each bit.
BCSP and BCSS bits determine the clock used by the main system
including the CPU and buses.
BCSP — Bus Clock Select PLL
0 = SYSCLK is derived from the crystal clock or from SLWCLK.
1 = SYSCLK source is the PLL.
Cannot be set when PLLON = 0. In limp-home mode, the output of
BCSP is forced to 1, but the BCSP bit reads the latched value.
BCSS — Bus Clock Select Slow
0 = SYSCLK is derived from the crystal clock EXTALi.
1 = SYSCLK source is the Slow clock SLWCLK.
This bit has no effect when BCSP is set.
MCS — Module Clock Select
0 = M clock is the same as PCLK.
1 = M clock is derived from Slow clock SLWCLK.
This bit determines the clock used by the ECT module and the baud
rate generators of the SCIs. In limp-home mode, the output of MCS is
forced to 0, but the MCS bit reads the latched value.
Bit 7
6
5
4
3
2
1
Bit 0
0
BCSP
BCSS
0
0
MCS
0
0
RESET:
0
0
0
0
0
0
0
0
CLKSEL
— Clock Generator Clock select Register
$003D
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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