参数资料
型号: ST72C314J4T1XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, FLASH, 8 MHz, MICROCONTROLLER, PQFP44
封装: TQFP-44
文件页数: 85/153页
文件大小: 2235K
代理商: ST72C314J4T1XXX
ST72334J/N, ST72314J/N, ST72124J
37/153
POWER SAVING MODES (Cont’d)
11.4 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).
11.4.1 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 (see Section
more details on the MCCSR register).
The MCU can exit ACTIVE-HALT mode on recep-
tion of either an MCC/RTC interrupt, a specific in-
page 34) or a RESET. When exiting ACTIVE-
HALT mode by means of a RESET or an interrupt,
a 4096 CPU cycle delay occurs. After the start up
delay, the CPU resumes operation by servicing
the interrupt or by fetching the reset vector which
woke it up (see Figure 23).
When entering ACTIVE-HALT mode, the I bit in
the CC register is cleared to enable interrupts.
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.
Figure 22. ACTIVE-HALT Timing Overview
Figure 23. ACTIVE-HALT Mode Flow-chart
Notes:
1. Peripheral clocked with an external clock source
can still be active.
2. Only the MCC/RTC interrupt and some specific
interrupts can exit the MCU from ACTIVE-HALT
mode (such as external interrupt). Refer to
details.
3. Before servicing an interrupt, the CC register is
pushed on the stack. The I bit of the CC register is
set during the interrupt routine and cleared when
the CC register is popped.
MCCSR
OIE bit
Power Saving Mode entered when HALT
instruction is executed
0
HALT mode
1
ACTIVE-HALT mode
HALT
RUN
4096 CPU CYCLE
DELAY
RESET
OR
INTERRUPT
HALT
INSTRUCTION
FETCH
VECTOR
ACTIVE
[MCCSR.OIE=1]
HALT INSTRUCTION
RESET
INTERRUPT 2)
Y
N
Y
CPU
OSCILLATOR
PERIPHERALS 1)
I BIT
ON
OFF
0
OFF
FETCH RESET VECTOR
OR SERVICE INTERRUPT
CPU
OSCILLATOR
PERIPHERALS 1)
I BIT
ON
OFF
X 3)
ON
CPU
OSCILLATOR
PERIPHERALS
I BITS
ON
X 3)
ON
4096 CPU CLOCK CYCLE
DELAY
(MCCSR.OIE=1)
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