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Technical Data
MC68HC11E Family — Rev. 4
130
Resets and Interrupts
MOTOROLA
Resets and Interrupts
5.7.1 Wait Mode
The WAI opcode places the MCU in wait mode, during which the CPU
registers are stacked and CPU processing is suspended until a qualified
interrupt is detected. The interrupt can be an external IRQ, an XIRQ, or
any of the internally generated interrupts, such as the timer or serial
interrupts. The on-chip crystal oscillator remains active throughout the
wait standby period.
The reduction of power in the wait condition depends on how many
internal clock signals driving on-chip peripheral functions can be shut
down. The CPU is always shut down during wait. While in the wait state,
the address/data bus repeatedly runs read cycles to the address where
the CCR contents were stacked. The MCU leaves the wait state when it
senses any interrupt that has not been masked.
The free-running timer system is shut down only if the I bit is set to 1 and
the COP system is disabled by NOCOP being set to 1. Several other
systems also can be in a reduced power-consumption state depending
on the state of software-controlled configuration control bits. Power
consumption by the analog-to-digital (A/D) converter is not affected
significantly by the wait condition. However, the A/D converter current
can be eliminated by writing the ADPU bit to 0. The SPI system is
enabled or disabled by the SPE control bit. The SCI transmitter is
enabled or disabled by the TE bit, and the SCI receiver is enabled or
disabled by the RE bit. Therefore, the power consumption in wait is
dependent on the particular application.
5.7.2 Stop Mode
Executing the STOP instruction while the S bit in the CCR is equal to 0
places the MCU in stop mode. If the S bit is not 0, the stop opcode is
treated as a no-op (NOP). Stop mode offers minimum power
consumption because all clocks, including the crystal oscillator, are
stopped while in this mode. To exit stop and resume normal processing,
a logic low level must be applied to one of the external interrupts (IRQ or
XIRQ) or to the RESET pin. A pending edge-triggered IRQ can also bring
the CPU out of stop.