st62t62b STMicroelectronics, st62t62b Datasheet - Page 29

• Manufacturer Part Number: st62t62b
• Description: 8-bit Otp/eprom Mcus With A/d Converter, Auto-reload Timer And Eeprom
• Manufacturer: STMicroelectronics

3.5 POWER SAVING MODES
The WAIT and STOP modes have been imple-
mented in the ST62xx family of MCUs in order to
reduce the product’s electrical consumption dur-
ing idle periods. These two power saving modes
are described in the following paragraphs.
3.5.1 WAIT Mode
The MCU goes into WAIT mode as soon as the
WAIT instruction is executed. The microcontroller
can be considered as being in a “software frozen”
state where the core stops processing the pro-
gram instructions, the RAM contents and periph-
eral registers are preserved as long as the power
supply voltage is higher than the RAM retention
voltage. In this mode the peripherals are still ac-
tive.
WAIT mode can be used when the user wants to
reduce the MCU power consumption during idle
periods, while not losing track of time or the capa-
bility of monitoring external events. The active os-
cillator is not stopped in order to provide a clock
signal to the peripherals. Timer counting may be
enabled as well as the Timer interrupt, before en-
tering the WAIT mode: this allows the WAIT mode
to be exited when a Timer interrupt occurs. The
same applies to other peripherals which use the
clock signal.
If the WAIT mode is exited due to a Reset (either
by activating the external pin or generated by the
Watchdog), the MCU enters a normal reset proce-
dure. If an interrupt is generated during WAIT
mode, the MCU’s behaviour depends on the state
of the processor core prior to the WAIT instruction,
but also on the kind of interrupt request which is
generated. This is described in the following para-
graphs. The processor core does not generate a
delay following the occurrence of the interrupt, be-
cause the oscillator clock is still available and no
stabilisation period is necessary.
3.5.2 STOP Mode
If the Watchdog is disabled, STOP mode is avail-
able. When in STOP mode, the MCU is placed in
the lowest power consumption mode. In this oper-
ating mode, the microcontroller can be considered
as being “frozen”, no instruction is executed, the
oscillator is stopped, the RAM contents and pe-
ripheral registers are preserved as long as the
power supply voltage is higher than the RAM re-
tention voltage, and the ST62xx core waits for the
occurrence of an external interrupt request or a
Reset to exit the STOP state.
If the STOP state is exited due to a Reset (by ac-
tivating the external pin) the MCU will enter a nor-
mal reset procedure. Behaviour in response to in-
terrupts depends on the state of the processor
core prior to issuing the STOP instruction, and
also on the kind of interrupt request that is gener-
ated.
This case will be described in the following para-
graphs. The processor core generates a delay af-
ter occurrence of the interrupt request, in order to
wait for complete stabilisation of the oscillator, be-
fore executing the first instruction.
ST62T52B ST62T62B/E62B
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