MC9S12NE64V1 Datasheet, PDF (166/554 Pages) Freescale Semiconductor, Inc – MC9S12NE64V1 Data Sheet

Chapter 4 Clocks and Reset Generator (CRGV4)
There are five different scenarios for the CRG to restart the MCU from wait mode:
• External reset
• Clock monitor reset
• COP reset
• Self-clock mode interrupt
• Real-time interrupt (RTI)
If the MCU gets an external reset during wait mode active, the CRG asynchronously restores all
configuration bits in the register space to its default settings and starts the reset generator. After completing
the reset sequence processing begins by fetching the normal reset vector. Wait mode is exited and the MCU
is in run mode again.
If the clock monitor is enabled (CME=1) the MCU is able to leave wait mode when loss of
oscillator/external clock is detected by a clock monitor fail. If the SCME bit is not asserted the CRG
generates a clock monitor fail reset (CMRESET). The CRG’s behavior for CMRESET is the same
compared to external reset, but another reset vector is fetched after completion of the reset sequence. If the
SCME bit is asserted the CRG generates a SCM interrupt if enabled (SCMIE=1). After generating the
interrupt the CRG enters self-clock mode and starts the clock quality checker (see Section 4.4.4, “Clock
Quality Checker”). Then the MCU continues with normal operation.If the SCM interrupt is blocked by
SCMIE = 0, the SCMIF flag will be asserted and clock quality checks will be performed but the MCU will
not wake-up from wait mode.
If any other interrupt source (e.g. RTI) triggers exit from wait mode the MCU immediately continues with
normal operation. If the PLL has been powered-down during wait mode the PLLSEL bit is cleared and the
MCU runs on OSCCLK after leaving wait mode. The software must manually set the PLLSEL bit again,
in order to switch system and core clocks to the PLLCLK.
If wait mode is entered from self-clock mode, the CRG will continue to check the clock quality until clock
check is successful. The PLL and voltage regulator (VREG) will remain enabled.
Table 4-11 summarizes the outcome of a clock loss while in wait mode.
MC9S12NE64 Data Sheet, Rev. 1.1
166
Freescale Semiconductor