PIC32MX320F032H_11 Datasheet, PDF (130/214 Pages) Microchip Technology – High-Performance, General Purpose and USB, 32-bit Flash Microcontrollers

PIC32MX3XX/4XX
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. See Section 26.2 “Watchdog
Timer (WDT)”.
If the interrupt priority is lower than or equal to current
priority, the CPU will remain halted, but the PBCLK will
start running and the device will enter into Idle mode.
Note: There is no FRZ mode for this module.
25.3.2 IDLE MODE
In the Idle mode, the CPU is halted but the System
clock (SYSCLK) source is still enabled. This allows
peripherals 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:
Changing the PBCLK divider ratio
requires recalculation of peripheral timing.
For example, assume the UART is config-
ured 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 fre-
quency 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 divi-
sor), the actual baud rate may be a tiny
percentage different than expected. For
this reason, any timing calculation
required for a peripheral should be per-
formed with the new PB clock frequency
instead of scaling the previous value
based on a change in PB divisor ratio.
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. How-
ever, when switching back to POSC, the
appropriate PLL and/or oscillator
startup/lock delays would be applied.
The device enters Idle mode when the SLPEN
(OSCCON<4>) bit 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
CPU. If the priority of the interrupt event is lower
than or equal to current priority of CPU, the CPU
will remain halted and the device will remain in
Idle mode.
• On any source of device Reset.
• On a WDT time-out interrupt. See Section 26.2
“Watchdog Timer (WDT)”.
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 con-
sumed by the peripherals. The PBCLK divisor is con-
trolled 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 USB, Interrupt Con-
troller, DMA, Bus Matrix and Prefetch Cache 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.
DS61143H-page 130
© 2011 Microchip Technology Inc.