PIC32MX1XX Datasheet, PDF (222/320 Pages) Microchip Technology – 32-bit Microcontrollers (up to 128 KB Flash and 32 KB SRAM) with Audio and Graphics Interfaces, USB, and Advanced Analog

PIC32MX1XX/2XX
The processor will exit, or ‘wake-up’, from Sleep on one
of the following events:
• On any interrupt from an enabled source that is
operating in Sleep. The interrupt priority must be
greater than the current CPU priority.
• On any form of device Reset.
• On a WDT time-out.
If the interrupt priority is lower than or equal to the
current priority, the CPU will remain Halted, but the
PBCLK will start running and the device will enter into
Idle mode.
25.3.2 IDLE MODE
In Idle mode, the CPU is Halted but the System Clock
(SYSCLK) source is still enabled. This allows peripher-
als to continue operation when the CPU is Halted.
Peripherals can be individually configured to Halt when
entering Idle by setting their respective SIDL bit.
Latency, when exiting Idle mode, is very low due to the
CPU oscillator source remaining active.
Note 1: Changing the PBCLK divider ratio
requires recalculation of peripheral tim-
ing. For example, assume the UART is
configured for 9600 baud with a PB clock
ratio of 1:1 and a POSC of 8 MHz. When
the PB clock divisor of 1:2 is used, the
input frequency to the baud clock is cut in
half; therefore, the baud rate is reduced
to 1/2 its former value. Due to numeric
truncation in calculations (such as the
baud rate divisor), the actual baud rate
may be a tiny percentage different than
expected. For this reason, any timing cal-
culation required for a peripheral should
be performed with the new PB clock fre-
quency instead of scaling the previous
value based on a change in the PB divisor
ratio.
2: Oscillator start-up and PLL lock delays
are applied when switching to a clock
source that was disabled and that uses a
crystal and/or the PLL. For example,
assume the clock source is switched from
POSC to LPRC just prior to entering Sleep
in order to save power. No oscillator start-
up delay would be applied when exiting
Idle. However, when switching back to
POSC, the appropriate PLL and/or
oscillator start-up/lock delays would be
applied.
The device enters Idle mode when the SLPEN bit
(OSCCON<4>) is clear and a WAIT instruction is
executed.
The processor will wake or exit from Idle mode on the
following events:
• On any interrupt event for which the interrupt
source is enabled. The priority of the interrupt
event must be greater than the current priority of
the CPU. If the priority of the interrupt event is
lower than or equal to current priority of the CPU,
the CPU will remain Halted and the device will
remain in Idle mode.
• On any form of device Reset
• On a WDT time-out interrupt
25.3.3 PERIPHERAL BUS SCALING
METHOD
Most of the peripherals on the device are clocked using
the PBCLK. The peripheral bus can be scaled relative to
the SYSCLK to minimize the dynamic power consumed
by the peripherals. The PBCLK divisor is controlled by
PBDIV<1:0> (OSCCON<20:19>), allowing SYSCLK to
PBCLK ratios of 1:1, 1:2, 1:4 and 1:8. All peripherals
using PBCLK are affected when the divisor is changed.
Peripherals such as the USB, Interrupt Controller, DMA,
and the bus matrix are clocked directly from SYSCLK.
As a result, they are not affected by PBCLK divisor
changes.
Changing the PBCLK divisor affects:
• The CPU to peripheral access latency. The CPU
has to wait for next PBCLK edge for a read to
complete. In 1:8 mode, this results in a latency of
one to seven SYSCLKs.
• The power consumption of the peripherals. Power
consumption is directly proportional to the fre-
quency at which the peripherals are clocked. The
greater the divisor, the lower the power consumed
by the peripherals.
To minimize dynamic power, the PB divisor should be
chosen to run the peripherals at the lowest frequency
that provides acceptable system performance. When
selecting a PBCLK divider, peripheral clock require-
ments, such as baud rate accuracy, should be taken
into account. For example, the UART peripheral may
not be able to achieve all baud rate values at some
PBCLK divider depending on the SYSCLK value.
DS61168D-page 222
Preliminary
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