Power Management
15-43
Clock Generation and System Reset Management
15.3.6.8
Functional Reset Generation
The ULPD generates the functional reset of the device internally from the
PWRON_RESET signal and holds it active low for a minimum of 20 REF_CK
(12-MHz) clock cycles.
15.3.7 32-kHz Oscillator
The 32-kHz oscillator is always on and uses a 32-kHz external quartz. The
modules working with the 32-kHz clock are:
-
32-kHz timer
-
Power management
-
UART communication with communication processor
-
PWL
-
MPUIO (debouncing)/keyboard (keypad)
15.3.8 12-MHz Oscillator
This oscillator is to be used with a 12-MHz external quartz, which is used by
the clock and reset management module and is provided to the clock ref of
DPLL1 for MPU, DSP, TC, and peripherals. It allows the generation of the
48 MHz required by USB, camera, MMC, and UARTs. The ULPD DPLL and
APLL, located in the ULPD, provide the 48 MHz. By default, the USB uses the
APLL. This 12-MHz clock is used as the input clock of the ULPD. The 12-MHz
oscillator is on during awake and big sleep mode. It is off during deep-sleep
mode. The power management module handles the wake-up sequence.
When using the on-chip oscillator (normal mode), either a 12-MHz crystal or
a 13-MHz crystal can be connected to the OSC1_IN and OSC1_OUT pins so
that the on-chip oscillator generates a 12-MHz or a 13-MHz clock reference
to the OMAP device. In external master mode, the on-chip oscillator is disabled
and a 12-MHz or 13-MHz reference clock must be provided by an external
oscillator connected to the OSC1_IN pin.
In both of these cases, the APLL can be configured to generate the 48-MHz
clock from either a 12-MHz or a 13-MHz reference clock. If a 13-MHz reference
clock is used, then use the APLL to generate the 48-MHz clock, as opposed
to using the ULPD DPLL. The ULPD DPLL can only generate a 48-MHz clock
when the reference is 12 MHz.
Note:
13-MHz Clock
If a 13-MHz reference clock is used, then any timings detailed in this docu-
ment (peripheral clocks, etc.) which are calculated based on the 12-MHz
reference clock must be recalculated using the 13-MHz value.