MC68HC11F1_13 Datasheet, PDF (79/158 Pages) Freescale Semiconductor, Inc – Technical Data

Freescale Semiconductor, Inc.
5.5.1 WAIT
The WAI opcode places the MCU in the WAIT condition, during which the CPU regis-
ters are stacked and CPU processing is suspended until a qualified interrupt is detect-
ed. 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 sig-
nals 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. Ensuring that the stack
contents are placed in internal RAM will further reduce power consumption. 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 one and the COP
system is disabled by NOCOP being set to one. Several other systems can also 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 zero. The SPI system is enabled or dis-
abled 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 con-
sumption in WAIT is dependent on the particular application.
5.5.2 STOP
Executing the STOP instruction while the S bit in the CCR is equal to zero places the
MCU in the STOP condition. If the S bit is not zero, the STOP opcode is treated as a
no-op (NOP). The STOP condition 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.
Because all clocks are stopped in this mode, all internal peripheral functions also stop.
The data in the internal RAM is retained as long as V_DD power is maintained. The CPU
state and I/O pin levels are static and are unchanged by STOP. Therefore, when an
interrupt restarts the system, the MCU resumes processing as if there were no inter-
ruption. If reset is used to restart the system a normal reset sequence results where
all I/O pins and functions are also restored to their initial states.
To use the IRQ pin as a means of recovering from STOP, the I bit in the CCR must be
clear (IRQ not masked). The XIRQ pin can be used to wake up the MCU from STOP
regardless of the state of the X bit in the CCR, although the recovery sequence de-
pends on the state of the X bit. If X is set to zero (XIRQ not masked), the MCU starts
up, beginning with the stacking sequence leading to normal service of the XIRQ re-
quest. If X is set to one (XIRQ masked or inhibited), then processing continues with
the instruction that immediately follows the STOP instruction, and no XIRQ interrupt
service is requested or pending.
TECHNICAL DATA
RESETS AND INTERRUPTS
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