ST7FLITE29 STMICROELECTRONICS [STMicroelectronics], ST7FLITE29 Datasheet - Page 40

• Manufacturer Part Number: ST7FLITE29
• Description: 8-BIT MCU WITH SINGLE VOLTAGE FLASH MEMORY, DATA EEPROM, ADC, TIMERS, SPI
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST7LITE2
POWER SAVING MODES (Cont’d)
9.4 HALT MODE
The HALT mode is the lowest power consumption
mode of the MCU. It is entered by executing the
‘HALT’ instruction when ACTIVE-HALT is disabled
(see
40/131
1
when the AWUEN bit in the AWUCSR register is
cleared.
The MCU can exit HALT mode on reception of ei-
ther a specific interrupt (see Table 5, “Interrupt
Mapping,” on page 35) or a RESET. When exiting
HALT mode by means of a RESET or an interrupt,
the oscillator is immediately turned on and the 256
or 4096 CPU cycle delay is used to stabilize the
oscillator. After the start up delay, the CPU
resumes operation by servicing the interrupt or by
fetching the reset vector which woke it up (see
ure
When entering HALT mode, the I bit in the CC reg-
ister is forced to 0 to enable interrupts. Therefore,
if an interrupt is pending, the MCU wakes up im-
mediately.
In HALT mode, the main oscillator is turned off
causing all internal processing to be stopped, in-
cluding the operation of the on-chip peripherals.
All peripherals are not clocked except the ones
which get their clock supply from another clock
generator (such as an external or auxiliary oscilla-
tor).
The compatibility of Watchdog operation with
HALT mode is configured by the “WDGHALT” op-
tion bit of the option byte. The HALT instruction
when executed while the Watchdog system is en-
abled, can generate a Watchdog RESET (see
tion 15.1 on page 123
Figure 24. HALT Timing Overview
[Active Halt disabled]
INSTRUCTION
RUN
25).
section 9.5 on page 41
HALT
HALT
256 OR 4096 CPU
CYCLE DELAY
INTERRUPT
for more details).
RESET
OR
for more details) and
VECTOR
FETCH
RUN
sec-
Fig-
Figure 25. HALT Mode Flow-chart
Notes:
1. WDGHALT is an option bit. See option byte sec-
tion for more details.
2. Peripheral clocked with an external clock source
can still be active.
3. Only some specific interrupts can exit the MCU
from HALT mode (such as external interrupt). Re-
fer to
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.
5. If the PLL is enabled by option byte, it outputs
the clock after a delay of t
(AWUCSR.AWUEN=0)
HALT INSTRUCTION
(Active Halt disabled)
N
WATCHDOG
WDGHALT
Table 5 Interrupt Mapping
RESET
1
INTERRUPT
Y
1)
ENABLE
3)
256 OR 4096 CPU CLOCK
OR SERVICE INTERRUPT
0
FETCH RESET VECTOR
OSCILLATOR
PERIPHERALS
CPU
OSCILLATOR
PERIPHERALS
CPU
OSCILLATOR
PERIPHERALS
CPU
I BIT
I BIT
I BIT
STARTUP
N
CYCLE
RESET
for more details.
Y
WATCHDOG
(see
DELAY
DISABLE
Figure
2)
OFF
OFF
OFF
OFF
5)
ON
ON
X
ON
ON
ON
X
0
4)
4)
12).