MC912DG128A Motorola, MC912DG128A Datasheet - Page 148

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

STOP exit in Limp
Home mode
without Delay
(Fast Stop
Recovery)
Clock Functions
MC68HC912DT128A Rev 2.0
148
CAUTION:
CAUTION:
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,
improper EXTALi clock cycles can occur on SYSCLK. This may lead to
a code runaway.
(NOLHM=0, CME=X, DLY=0)
Fast STOP recovery refers to any exit from STOP using DLY=0.
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, it is possible to exit STOP with the DLY
bit cleared. In this case, STOP is de-asserted without delay and the MCU
will execute software in limp-home mode, giving the crystal oscillator
time to stablise.
This mode is not recommended since the risk of the clock monitor
detecting incorrect clocks is high.
Clock Functions
MOTOROLA
14-clock