MC9S12XD256MAL Datasheet, PDF (109/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Chapter 2 Clocks and Reset Generator (S12CRGV6)
2.4.3.3.1 Wake-up from Pseudo Stop Mode (PSTP=1)
Wake-up from pseudo stop mode is the same as wake-up from wait mode. There are also four different
scenarios for the CRG to restart the MCU from pseudo stop mode:
• External reset
• Clock monitor fail
• COP reset
• Wake-up interrupt
If the MCU gets an external reset or COP reset during pseudo stop 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 or COP reset vector. pseudo stop
mode is left and the MCU is in run mode again.
If the clock monitor is enabled (CME = 1), the MCU is able to leave pseudo stop 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 (Section 2.4.1.4, “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 but the CRG will not wake-up from pseudo stop mode.
If any other interrupt source (e.g., RTI) triggers exit from pseudo stop mode, the MCU immediately
continues with normal operation. Because the PLL has been powered-down during stop mode, the
PLLSEL bit is cleared and the MCU runs on OSCCLK after leaving stop mode. The software must set the
PLLSEL bit again, in order to switch system and core clocks to the PLLCLK.
Table 2-13 summarizes the outcome of a clock loss while in pseudo stop mode.
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor
109