ST72F264G ST Microelectronics, ST72F264G Datasheet - Page 35

• Manufacturer Part Number: ST72F264G
• Description: (ST72F260G - ST72F264G) 8-BIT MCU
• Manufacturer: ST Microelectronics

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DataSheet
8.4 ACTIVE-HALT AND HALT MODES
ACTIVE-HALT and HALT modes are the two low-
est power consumption modes of the MCU. They
are both entered by executing the ‘HALT’ instruc-
tion. The decision to enter either in ACTIVE-HALT
or HALT mode is given by the MCC/RTC interrupt
enable flag (OIE bit in MCCSR register).
8.4.1 ACTIVE-HALT MODE
ACTIVE-HALT mode is the lowest power con-
sumption mode of the MCU with a real time clock
available. It is entered by executing the ‘HALT’ in-
struction when the OIE bit of the Main Clock Con-
troller Status register (MCCSR) is set.
The MCU can exit ACTIVE-HALT mode on recep-
tion of either an MCC/RTC interrupt, a specific in-
terrupt (see
32) or a RESET. When exiting ACTIVE-HALT
mode by means of an interrupt, no 4096 CPU cy-
cle delay occurs. The CPU resumes operation by
servicing the interrupt or by fetching the reset vec-
tor which woke it up (see
When entering ACTIVE-HALT mode, the I[1:0] bits
in the CC register are forced to ‘10b’ to enable in-
terrupts. Therefore, if an interrupt is pending, the
MCU wakes up immediately.
In ACTIVE-HALT mode, only the main oscillator
and its associated counter (MCC/RTC) are run-
ning to keep a wake-up time base. All other periph-
erals are not clocked except those which get their
clock supply from another clock generator (such
as external or auxiliary oscillator).
The safeguard against staying locked in ACTIVE-
HALT mode is provided by the oscillator interrupt.
Note: As soon as the interrupt capability of one of
the oscillators is selected (MCCSR.OIE bit set),
entering ACTIVE-HALT mode while the Watchdog
is active does not generate a RESET.
This means that the device cannot spend more
than a defined delay in this power saving mode.
MCCSR
OIE bit
0
1
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HALT mode
ACTIVE-HALT mode
Power Saving Mode entered when HALT
Table 5, “Interrupt Mapping,” on page
instruction is executed
Figure
25).
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Figure 24. ACTIVE-HALT Timing Overview
Figure 25. ACTIVE-HALT Mode Flowchart
Notes:
1. This delay occurs only if the MCU exits ACTIVE-
HALT mode by means of a RESET.
2. Peripheral clocked with an external clock source
can still be active.
3. Only the MCC/RTC interrupt and some specific
interrupts can exit the MCU from ACTIVE-HALT
mode (such as external interrupt). Refer to
5, “Interrupt Mapping,” on page 32
4. 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 restored when the CC
register is popped.
[MCCSR.OIE=1]
INSTRUCTION
HALT INSTRUCTION
RUN
N
(MCCSR.OIE=1)
HALT
INTERRUPT
ACTIVE
HALT
ST72260G, ST72262G, ST72264G
Y
CYCLE DELAY
INTERRUPT
3)
4096 CPU
RESET
OR SERVICE INTERRUPT
FETCH RESET VECTOR
OR
OSCILLATOR
PERIPHERALS
CPU
I[1:0] BITS
OSCILLATOR
PERIPHERALS
CPU
I[1:0] BITS
OSCILLATOR
PERIPHERALS
CPU
I[1:0] BITS
N
4096 CPU CLOCK
CYCLE DELAY
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RESET
Y
1)
for more details.
VECTOR
FETCH
RUN
2)
XX
XX
OFF
OFF
OFF
ON
ON
ON
ON
ON
ON
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4)
4)
Table
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