MC68HC912D60 Motorola, MC68HC912D60 Datasheet - Page 150

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MC68HC912D60

Manufacturer Part Number
MC68HC912D60
Description
Microcontrollers
Manufacturer
Motorola
Datasheet
Clock Functions
11.6.5 Executing the STOP instruction without Limp Home mode, clock monitor enabled
11.6.6 STOP exit in Limp Home mode with Delay
Technical Data
150
CAUTION:
(NOLHM=1, CME=1, DLY=X)
If the NOLHM bit and the CME (or FCME) bits are set, a clock monitor
failure is detected when a STOP instruction is executed and the MCU
resets via the clock monitor reset vector.
(NOLHM=0, CME=X, DLY=1)
If the NOLHM bit is cleared, then the CME (or FCME) bit is masked when
a STOP instruction is executed to prevent a clock monitor failure. When
coming out of STOP mode, the MCU goes into limp-home mode where
CME and FCME signals are asserted.
When using a crystal oscillator, a normal STOP exit sequence requires
the DLY bit to be set to allow for the crystal stabilization period.
With the 13-stage counter clocked by the VCO (at f
delay of 4096 XCLK cycles at the limp-home frequency, if the clock
monitor indicates the presence of an external clock, the limp-home mode
is de-asserted and the MCU exits STOP normally using EXTALi clock.
Where the crystal start-up time is longer than the initial count of 4096
XCLK cycles, or in the absence of an external clock, the MCU recovers
from STOP following the 4096 count in limp-home mode with both the
LHOME flag set and the LHIF limp-home interrupt request set to indicate
it is not operating at the desired frequency. Each time the 13-stage
counter reaches a count of 4096 XCLK cycles, a check of the clock
monitor status is performed.
When the presence of an external clock is detected, limp-home mode is
exited and the LHOME flag is cleared. This sets the limp-home interrupt
flag and if enabled by the LHIE bit, the limp-home mode interrupt is
requested.
The clock monitor circuit can be misled by EXTALi clock into reporting a
good signal before it has fully stabilised. Under these conditions,
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
Clock Functions
MC68HC912D60A — Rev 3.0
VCOMIN
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MOTOROLA

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