MOTOROLA
Chapter 7. Power Management
7-11
Functional Description
If the phase lock loop (PLL) in the clock module is active and if the appropriate (LOCRE,
LOLRE) bits in the synthesizer control register are set, then any loss-of-clock or
loss-of-lock will reset the chip and exit any low-power modes.
If the watchdog timer is still enabled during wait or doze modes, then a watchdog timer
timeout may generate a reset to exit these low-power modes.
When the CPU is inactive, a software reset cannot be generated to exit any low-power
mode.
7.3.2.16 Chip Configuration Module
The Chip Configuration Module is unaffected by entry into a low-power mode. If
low-power mode is exited by a reset, chip configuration may be executed if configured to
do so.
7.3.2.17 Clock Module
In wait and doze modes, the clocks to the CPU, Flash, and SRAM will be stopped and the
system clocks to the peripherals are enabled. Each module may disable the module clocks
locally at the module level. In stop mode, all clocks to the system will be stopped.
During stop mode, there are several options for enabling/disabling the PLL and/or crystal
oscillator (OSC); each of these options requires a compromise between wakeup recovery
time and stop mode power. The PLL may be disabled during stop mode. A wakeup time of
up to 200
µ
s is required for the PLL to re-lock. The OSC may also be disabled during stop
mode. The time required for the OSC to restart is dependent upon the startup time of the
crystal used. Power consumption can be reduced in stop mode by disabling either or both
of these functions via the SYNCR[STMPD] bits.
The external CLKOUT signal may be enabled during low-power stop (if the PLL is still
enabled) to support systems using this signal as the clock source.
The system clocks may be enabled during wakeup from stop mode without waiting for the
PLL to lock. This eliminates the wakeup recovery time, but at the risk of sending a
potentially unstable clock to the system. It is recommended, if this option is used, that the
PLL frequency divider is set so that the targeted system frequency is no more than half the
maximum allowed. This will allow for any frequency overshoot of the PLL while still
keeping the system clock within specification.
In external clock mode, there are no wait times for the OSC startup or PLL lock.
During wakeup from stop mode, the Flash clock will always clock through 16 cycles before
the system clocks are enabled. This allows the Flash module time to recover from the
low-power mode. Thus, software may immediately continue to fetch instructions from the
Flash memory.
Summary of Contents for ColdFire MCF5281
Page 124: ...3 20 MCF5282 User s Manual MOTOROLA EMAC Instruction Set Summary ...
Page 141: ...MOTOROLA Chapter 5 Static RAM SRAM 5 5 SRAM Programming Model ...
Page 142: ...5 6 MCF5282 User s Manual MOTOROLA SRAM Programming Model ...
Page 168: ...6 26 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 186: ...7 18 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 228: ...9 22 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 246: ...10 18 MCF5282 User s Manual MOTOROLA Low Power Wakeup Operation ...
Page 254: ...11 8 MCF5282 User s Manual MOTOROLA Memory Map and Registers ...
Page 264: ...12 10 MCF5282 User s Manual MOTOROLA Chip Select Registers ...
Page 280: ...13 16 MCF5282 User s Manual MOTOROLA Misaligned Operands ...
Page 314: ...14 34 MCF5282 User s Manual MOTOROLA MCF5282 External Signals ...
Page 339: ...MOTOROLA Chapter 15 Synchronous DRAM Controller Module 15 25 SDRAM Example ...
Page 340: ...15 26 MCF5282 User s Manual MOTOROLA SDRAM Example ...
Page 356: ...16 16 MCF5282 User s Manual MOTOROLA DMA Controller Module Functional Description ...
Page 408: ...17 52 MCF5282 User s Manual MOTOROLA Buffer Descriptors ...
Page 446: ...20 24 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 474: ...22 18 MCF5282 User s Manual MOTOROLA Programming Model ...
Page 510: ...23 36 MCF5282 User s Manual MOTOROLA Operation ...
Page 526: ...24 16 MCF5282 User s Manual MOTOROLA I2C Programming Examples ...
Page 672: ...28 12 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 718: ...29 46 MCF5282 User s Manual MOTOROLA Motorola Recommended BDM Pinout ...
Page 750: ...32 8 MCF5282 User s Manual MOTOROLA Ordering Information ...