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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
50 of 808
NXP Semiconductors
UM10360
Chapter 4: LPC17xx Clocking and power control
8.
Power control
The LPC17xx supports a variety of power control features: Sleep mode, Deep Sleep
mode, Power-down mode, and Deep Power-down mode. The CPU clock rate may also be
controlled as needed by changing clock sources, re-configuring PLL values, and/or
altering the CPU clock divider value. This allows a trade-off of power versus processing
speed based on application requirements. In addition, Peripheral Power Control allows
shutting down the clocks to individual on-chip peripherals, allowing fine tuning of power
consumption by eliminating all dynamic power use in any peripherals that are not required
for the application.
Entry to any reduced power mode begins with the execution of either a WFI (Wait For
Interrupt) or WFE (Wait For Exception) instruction by the Cortex-M3. The Cortex-M3
internally supports two reduced power modes: Sleep and Deep Sleep. These are selected
by the SLEEPDEEP bit in the cortex-M3 System Control Register. Power-down and Deep
Power-down modes are selected by bits in the PCON register. See
. The same
register contains flags that indicate whether entry into each reduced power mode actually
occurred.
The LPC17xx also implements a separate power domain in order to allow turning off
power to the bulk of the device while maintaining operation of the Real Time Clock.
Reduced power modes have some limitation during debug, see
for more
information.
8.1 Sleep mode
Note:
Sleep mode on the LPC17xx corresponds to the Idle mode on LPC2xxx series
devices. The name is changed because ARM has incorporated portions of reduced power
mode control into the Cortex-M3. LPC17xx documentation uses the Cortex-M3
terminology where applicable.
When Sleep mode is entered, the clock to the core is stopped, and the SMFLAG bit in
PCON is set, see
.Resumption from the Sleep mode does not need any
special sequence but re-enabling the clock to the ARM core.
In Sleep mode, execution of instructions is suspended until either a Reset or an interrupt
occurs. Peripheral functions continue operation during Sleep mode and may generate
interrupts to cause the processor to resume execution. The GPDMA may operate in Sleep
Table 42.
Peripheral Clock Selection register bit values
PCLKSEL0 and PCLKSEL1
individual peripheral’s clock
select options
Function
Reset
value
00
PCLK_peripheral = CCLK/4
00
01
PCLK_peripheral = CCLK
10
PCLK_peripheral = CCLK/2
11
PCLK_peripheral = CCLK/8 except for CAN1, CAN2, and
CAN filtering when “11” selects
PCLK_CAN1/PCLK1_CAN2/PCLK_ACF = CCLK/6.