EP7209 Datasheet, PDF (20/128 Pages) Cirrus Logic – Ultra-Low-Power Audio Decoder System-on-Chip

EP7209
3.2 State Control
The EP7209 supports the following Power Man-
agement States: Operating, Idle, and Standby (see
Figure 3). The normal program execution state is
the Operating State; this is a full performance state
where all of the clocks and peripheral logic are en-
abled. The Idle State is the same as the Operating
State with the exception of the CPU clock being
halted, and an interrupt or wakeup will return it
back to the Operating State. The Standby State has
the lowest power consumption, selecting this mode
shuts down the main oscillator, leaving only the
Real Time Clock and its associated logic powered.
It is important when the EP7209 is in Standby that
all power and ground pins remain connected to
power and ground in order to have a proper system
wake-up. The only state that Standby can transition
to is the Operating State.
Standby
Interrupt or rising wakeup
Write to standby location,
power fail, or user reset
Operating
nPOR, power fail,
or user reset
Interrupt
Write to halt location
Idle
Figure 3. State Diagram
In the description below, the RUN/CLKEN pin can
be used either for the RUN functionality, or the
CLKEN functionality to allow an external oscilla-
tor to be disabled in the 13 MHz mode. Either RUN
or CLKEN functionality can be selected according
to the state of the CLKENSL bit in the SYSCON2
register. Table 7 on the following page shows pe-
ripheral status in various power management
states.
3.2.1 Standby State
The Standby State equates to the system being
switched "off" (i.e., no display, and the main oscil-
lator is shut down). When the 18.432–73.72 MHz
mode is selected, the PLL will be shut down. In the
13 MHz mode, if the CLKENSL bit is set low, then
the CLKEN signal will be forced low and can, if re-
quired, be used to disable an external oscillator.
In the Standby State, all the system memory and
state is maintained and the system time is kept up-
to-date. The PLL/on-chip oscillator or external os-
cillator is disabled and the system is static, except
for the low power watch crystal (32 kHz) oscillator
and divider chain to the RTC and LED flasher. The
RUN signal is driven low and this signal can be
used externally in the system to power down other
system modules.
Whenever the EP7209 is in the Standby State, the
external address and data buses are forced low in-
ternally by the RUN signal. This is done to prevent
peripherals that are powered-down from draining
current. Also, the internal peripheral’s signals get
set to their Reset State.
When first powered, or reset by the nPOR (Power
On Reset, active low) signal, the EP7209 is forced
into the Standby State. This is known as a cold re-
set, and when leaving the Standby State after a cold
reset, external wake up is the only way to wake up
the device. When leaving the Standby State after
non-cold reset conditions (i.e., the software has
forced the device into the Standby State), the tran-
sition to the Operating State can be caused by a ris-
ing edge on the WAKEUP input signal or by an
enabled interrupt. Normally, when entering the
Standby State from the Operating State, the soft-
ware will leave some interrupt sources enabled.
NOTE:
The CPU cannot be awakened by the TINT,
WEINT, and BLINT interrupts when in the
Standby State.
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