ST72325S6B6 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
ST72325S6B6
STMicroelectronics
'ST72325S6B6' PDF : 196 Pages View PDF
ST72325
POWER SAVING MODES (Cont’d)
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).
MCCSR Power Saving Mode entered when HALT
OIE bit
instruction is executed
0 HALT mode
1 ACTIVE-HALT mode
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 (see section
10.2 on page 61 for more details on the MCCSR
register).
The MCU can exit ACTIVE-HALT mode on recep-
tion of an external interrupt, MCC/RTC interrupt or
a RESET. When exiting ACTIVE-HALT mode by
means of an interrupt, no 256 or 4096 CPU cycle
delay occurs. The CPU resumes operation by
servicing the interrupt or by fetching the reset vec-
tor which woke it up (see Figure 30).
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.
CAUTION: When exiting ACTIVE-HALT mode fol-
lowing an MCC/RTC interrupt, OIE bit of MCCSR
register must not be cleared before tDELAY after
the interrupt occurs (tDELAY = 256 or 4096 tCPU de-
lay depending on option byte). Otherwise, the ST7
enters HALT mode for the remaining tDELAY peri-
od.
Figure 29. ACTIVE-HALT Timing Overview
ACTIVE 256 OR 4096 CPU
RUN HALT CYCLE DELAY 1)
RUN
HALT
INSTRUCTION
[MCCSR.OIE=1]
RESET
OR
INTERRUPT
FETCH
VECTOR
Figure 30. ACTIVE-HALT Mode Flow-chart
HALT INSTRUCTION
(MCCSR.OIE=1)
OSCILLATOR
PERIPHERALS 2)
CPU
I[1:0] BITS
ON
OFF
OFF
10
N
INTERRUPT
Y
N
RESET
Y
OSCILLATOR
PERIPHERALS
CPU
I[1:0] BITS
ON
OFF
ON
XX 3)
256 OR 4096 CPU CLOCK
CYCLE DELAY
OSCILLATOR
PERIPHERALS
CPU
I[1:0] BITS
ON
ON
ON
XX 3)
FETCH RESET VECTOR
OR SERVICE INTERRUPT
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. 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.
47/193
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