MC9S08QE16CLC Datasheet, PDF (38/350 Pages) Freescale Semiconductor, Inc – Low-power wireless applications, Gas, water and heater meters

Chapter 3 Modes of Operation
writing to PPDACK, the pins will be controlled by their associated port control registers when the I/O
latches are opened.
A separate self-clocked source (1 kHz) for the real-time interrupt allows a wakeup from stop2 or stop3
mode with no external components. When RTIS2:RTIS1:RTIS0 = 0:0:0, the real-time interrupt function
and this 1-kHz source are disabled. Power consumption is lower when the 1-kHz source is disabled, but in
that case the real-time interrupt cannot wake the MCU from stop.
3.6.2 Stop3 Mode
To enter stop3, the user must execute a STOP instruction with stop3 selected (PPDC = 0) and stop mode
enabled (STOPE = 1). Upon entering the stop3 mode, all of the clocks in the MCU, including the oscillator
itself, are halted. The ICG enters its standby state, as does the voltage regulator and the ADC. The states
of all of the internal registers and logic, as well as the RAM content, are maintained. The I/O pin states are
not latched at the pin as in stop2. Instead they are maintained by virtue of the states of the internal logic
driving the pins being maintained.
Exit from stop3 is done by asserting RESET, an asynchronous interrupt pin, or through the real-time
interrupt (RTI). The asynchronous interrupt pins are the IRQ or KBI pins. Exit from stop3 can also
facilitated by the SCI reciever interrupt, the ADC, and LVI.
If stop3 is exited by means of the RESET pin, then the MCU will be reset and operation will resume after
taking the reset vector. Exit by means of an asynchronous interrupt or the real-time interrupt will result in
the MCU taking the appropriate interrupt vector.
A separate self-clocked source (1 kHz) for the real-time interrupt allows a wakeup from stop2 or stop3
mode with no external components. When RTIS2:RTIS1:RTIS0 = 0:0:0, the real-time interrupt function
and this 1-kHz source are disabled. Power consumption is lower when the 1-kHz source is disabled, but in
that case the real-time interrupt cannot wake the MCU from stop.
3.6.3 Active BDM Enabled in Stop Mode
Entry into the active background mode from run mode is enabled if the ENBDM bit in BDCSCR is set.
This register is described in Chapter 16, “Development Support” of this data sheet. If ENBDM is set when
the CPU executes a STOP instruction, the system clocks to the background debug logic remain active
when the MCU enters stop mode so background debug communication is still possible. In addition, the
voltage regulator does not enter its low-power standby state but maintains full internal regulation. If the
user attempts to enter stop2 with ENBDM set, the MCU will instead enter stop3.
Most background commands are not available in stop mode. The memory-access-with-status commands
do not allow memory access, but they report an error indicating that the MCU is in either stop or wait
mode. The BACKGROUND command can be used to wake the MCU from stop and enter active
background mode if the ENBDM bit is set. After entering background debug mode, all background
commands are available. Table 3-2 summarizes the behavior of the MCU in stop when entry into the
background debug mode is enabled.
MC9S08AC60 Series Data Sheet, Rev. 3
38
Freescale Semiconductor