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MCU Modes of Operation
MC1321x Reference Manual, Rev. 1.1
Freescale Semiconductor
10-5
10.6.3
Stop3 Mode
Upon entering the Stop3 Mode, all of the clocks in the MCU, including the oscillator itself, are halted. The
ICG is turned off, the ATD is disabled, and the voltage regulator is put in standby. 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 performed by asserting RESET, an asynchronous interrupt pin, or through the real-time
interrupt. The asynchronous interrupt pins are the IRQ or KBI pins.
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 wake up 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.
10.6.4
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.
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
either Stop1 or 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 the device enters background debug mode, all
background commands are available. The table below summarizes the behavior of the MCU in stop when
entry into the background debug mode is enabled.
Table 10-2. BDM Enabled Stop Mode Behavior
Mode
PDC
PPDC
CPU, Digital
Peripherals,
FLASH
RAM
ICG
ATD
Regulator
I/O Pins
RTI
Stop3
Don’t
care
Don’t
care
Standby
Active
Disabled1
1 Either ATD Stop Mode or Power-Down Mode depending on the state of ATDPU.
Active
States held
Optionally on