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Power saving modes
ST7LITEUS2, ST7LITEUS5
Figure 22.
Active-halt mode flowchart
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.
8.4.2 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 mode is disabled.
The MCU can exit Halt mode on reception of either a specific interrupt (see
) or a reset. When exiting Halt mode by means of a reset or an interrupt,
the main oscillator is immediately turned on and the 64 CPU cycle delay is used to stabilize
it. After the start up delay, the CPU resumes operation by servicing the interrupt or by
fetching the reset vector which woke it up (see
When entering Halt mode, the I bit in the CC register is forced to 0 to enable interrupts.
Therefore, if an interrupt is pending, the MCU wakes immediately.
In Halt mode, the main oscillator is turned off causing all internal processing to be stopped,
including 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 oscillator).
The compatibility of watchdog operation with Halt mode is configured by the “WDGHALT”
option bit of the option byte. The HALT instruction when executed while the watchdog
system is enabled, can generate a watchdog reset (see
for more
details).
HALT
INSTRUCTION
RESET
INTERRUPT
3)
Y
N
N
Y
CPU
OSCILLATOR
PERIPHERALS
2)
I BIT
ON
OFF
0
OFF
FETCH RESET VECTOR
OR SERVICE INTERRUPT
CPU
OSCILLATOR
PERIPHERALS
2)
I BIT
ON
OFF
X
4)
ON
CPU
OSCILLATOR
PERIPHERALS
I BITS
ON
ON
X
4)
ON
64 CPU CLOCK CYCLE
DELAY
(Active-halt enabled)
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