Datasheet

ST72321Rx ST72321ARx ST72321Jx
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POWER SAVING MODES (Cont’d)
8.3 WAIT MODE
WAIT mode places the MCU in a low power con-
sumption mode by stopping the CPU.
This power saving mode is selected by calling the
‘WFI’ instruction.
All peripherals remain active. During WAIT mode,
the I[1:0] bits of the CC register are forced to ‘10’,
to enable all interrupts. All other registers and
memory remain unchanged. The MCU remains in
WAIT mode until an interrupt or RESET occurs,
whereupon the Program Counter branches to the
starting address of the interrupt or Reset service
routine.
The MCU will remain in WAIT mode until a Reset
or an Interrupt occurs, causing it to wake up.
Refer to Figure 25.
Figure 25. WAIT Mode Flow-chart
Note:
1. Before servicing an interrupt, the CC register is
pushed on the stack. The I[1:0] bits of the CC reg-
ister are set to the current software priority level of
the interrupt routine and recovered when the CC
register is popped.
WFI INSTRUCTION
RESET
INTERRUPT
Y
N
N
Y
CPU
OSCILLATOR
PERIPHERALS
I[1:0] BITS
ON
ON
10
OFF
FETCH RESET VECTOR
OR SERVICE INTERRUPT
CPU
OSCILLATOR
PERIPHERALS
I[1:0] BITS
ON
OFF
10
ON
CPU
OSCILLATOR
PERIPHERALS
I[1:0] BITS
ON
ON
XX
1)
ON
256 OR 4096 CPU CLOCK
CYCLE DELAY