
Power Mode Controls
MOTOROLA
System Integration Module (SIM)
4-15
Preliminary
4
3. Functions disabled in Stop mode:
— DSP56800E core
— all system clocks
— peripheral bus clock
— PLL optionally
— OSC optionally
All system clocks continue running in the Wait mode, allowing the DMA to operate in the
Wait mode. The time-based clock generated by the oscillator and Clock Generation
Module (CGM) are not affected by Low Power modes. Time based functions such as a
Time of Day (TOD) module and Computer Operating Properly (COP) module must be
individually disabled for maximum low-power effects. Likewise, Power Mode Controls
do not affect pull-up/pull-down resistor enabling. Power loss through input and
bidirectional I/O cell pull-up/pull-down resistors can be eliminated by disabling the
resistor in the software where supported, or in the case of bidirectional I/O, by putting the
cell in an output state and avoiding external contention.
When the core executes a Stop or Wait instruction it will wait until any stall or hold off
activity has completed (c7WAITST has deasserted) then assert the p5STOP or p5WAIT
SIM input and the SIM will enter the corresponding low power mode. The SIM control
register also contains Stop and Wait disable bits, and feed the core. When asserted, these
cause the core to ignore Stop and Wait instructions, not assert p5STOP or p5WAIT.
Recovery from Stop or Wait mode to Run mode occurs if there is a pending enabled
interrupt (INT_PEND input asserts), or if there is a Debug mode request from the core due
to a JTAG initiated Debug mode entry request (JTDEBREQ input asserts), or if there is a
Debug mode entry request from the DE input pin (DE asserts). These three inputs are
asynchronous so they are metastabilized and re-timed to the system clock domain before
use.
The SIM has special control relationships with both the Oscillator (OSC) module and the
Phase Locked Loop (PLL) module. By default, the SIM provides an extreme low power
Stop mode (when OMR6_SD set to zero), by shutting down the PLL and, if possible, the
oscillator output amplifiers. Alternatively (when OMR6_SD set to one), the SIM supports
a fast Stop mode recovery and does not affect the state of the PLL or oscillator when the
Stop mode is entered.
Extreme low power Stop mode works in this manner: upon entering the Stop mode, the
SIM asserts its PLL_SHUTDOWN output causing the PLL to be disabled and bypassed.
One cycle later, it asserts its OSC_LOPWR output. This feeds the LOW_PWR_MODE
input of the OSC. When the TOD clock prescaler in the OSC module is used (TOD_SEL