Freescale Semiconductor, Inc.
Clock Functions
(NOLHM=1, CME=0, DLY=0)
If NOLHM is set to 1 and the CME and FCME bits are cleared, the limp
home clock is not used. In this mode, crystal activity is the only method
by which the device may recover from Pseudo-STOP. The device will
start execution with the EXTALi clock following 16 XCLK cycles.
CAUTION: Due to switching of the clock this configuration is not recommended.
11.6.13 Summary of STOP and pseudo-STOP Mode Exit Conditions
Table 11-1 and Table 11-2 summarise the exit conditions from STOP
and pseudo-STOP modes using Interrupt, Key-interrupt and XIRQ.
A short RESET pulse should not be used to exit stop or pseudo-STOP
mode because Limp Home mode is automatically entered after RESET
(when VDDPLL=VDD). The RESET wakeup pulse must be longer than the
oscillator startup time (as in power on reset) in order to remove the risk
of code runaway.
. .
Table 11-1. Summary of STOP Mode Exit Conditions
Mode
Conditions
Summary
STOP exit without Limp Home
mode,
NOLHM=1
CME=0
Oscillator must be stable within 4096 XCLK cycles. XCLK
can be modified by SLOW divider register.
clock monitor disabled
DLY=X
Use of DLY=0 only recommended with external clock.
Executing the STOP instruction
without Limp Home mode,
clock monitor enabled
NOLHM=1
CME=1
DLY=X
When a STOP instruction is executed the MCU resets via
the clock monitor reset vector.
Oscillator must be stable within 4096
fVCOMIN cycles or there is a possibility of code runaway as
the clock monitor circuit can be misled by EXTALi clock
into reporting a good signal before it has fully stabilised
NOLHM=0
CME=X
DLY=1
STOP exit in Limp Home mode
with Delay
STOP exit in Limp Home mode
without Delay (Fast Stop
Recovery)
NOLHM=0
CME=X
DLY=0
This mode is only recommended for use with an external
clock source.
Technical Data
MC68HC912DG128 — Rev 3.0
Clock Functions
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