Datasheet

ST7LITE0xY0, ST7LITESxY0
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POWER SAVING MODES (Cont’d)
9.4 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 LTCSR/ATCSR reg-
ister status as shown in the following table:.
9.4.1 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 active halt mode is enabled.
The MCU can exit ACTIVE-HALT mode on recep-
tion of a Lite Timer / AT Timer interrupt or a RE-
SET.
– When exiting ACTIVE-HALT mode by means of
a RESET, a 256 CPU cycle delay occurs. After
the start up delay, the CPU resumes operation
by fetching the reset vector which woke it up (see
Figure 26).
– When exiting ACTIVE-HALT mode by means of
an interrupt, the CPU immediately resumes oper-
ation by servicing the interrupt vector which woke
it up (see Figure 26).
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 the selected timer counter (LT/AT) are running
to keep a wake-up time base. All other peripherals
are not clocked except those which get their clock
supply from another clock generator (such as ex-
ternal or auxiliary oscillator).
Caution: As soon as ACTIVE-HALT is enabled,
executing a HALT instruction while the Watchdog
is active does not generate a RESET if the
WDGHALT bit is reset.
This means that the device cannot spend more
than a defined delay in this power saving mode.
Figure 25. ACTIVE-HALT Timing Overview
Figure 26. ACTIVE-HALT Mode Flow-chart
Notes:
1. This delay occurs only if the MCU exits ACTIVE-
HALT mode by means of a RESET.
2. Peripherals clocked with an external clock
source can still be active.
3. Only the Lite Timer RTC and AT Timer interrupts
can exit the MCU from ACTIVE-HALT mode.
4. 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.
LTCSR
TBIE bit
ATCSR
OVFIE
bit
ATCSR
CK1 bit
ATCSR
CK0 bit
Meaning
0xx0
ACTIVE-HALT
mode disabled
00xx
0111
1xxx
ACTIVE-HALT
mode enabled
x101
HALTRUN RUN
256 CPU
CYCLE DELAY
1)
RESET
OR
INTERRUPT
HALT
INSTRUCTION
FETCH
VECTOR
ACTIVE
[Active Halt Enabled]
HALT INSTRUCTION
RESET
INTERRUPT
3)
Y
N
N
Y
CPU
OSCILLATOR
PERIPHERALS
2)
IBIT
ON
OFF
0
OFF
FETCH RESET VECTOR
OR SERVICE INTERRUPT
CPU
OSCILLATOR
PERIPHERALS
2)
IBIT
ON
OFF
X
4)
ON
CPU
OSCILLATOR
PERIPHERALS
IBITS
ON
ON
X
4)
ON
256 CPU CLOCK CYCLE
DELAY
(Active Halt enabled)
1