LPC2478 NXP Semiconductors, LPC2478 Datasheet - Page 47

• Manufacturer Part Number: LPC2478
• Description: NXP Semiconductors designed the LPC2478 microcontroller, powered by theARM7TDMI-S core, to be a highly integrated microcontroller for a wide range ofapplications that require advanced communications and high quality graphic displays
• Manufacturer: NXP Semiconductors

NXP Semiconductors
LPC2478
Product data sheet
7.26.4.1 Idle mode
7.26.4.2 Sleep mode
7.26.4.3 Power-down mode
7.26.4 Power control
The LPC2478 supports a variety of power control features. There are four special modes
of processor power reduction: Idle mode, Sleep mode, Power down-mode and Deep
power-down mode. The CPU clock rate may also be controlled as needed by changing
clock sources, reconfiguring 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. Each of the peripherals
has its own clock divider which provides even better power control.
The LPC2478 also implements a separate power domain in order to allow turning off
power to the bulk of the device while maintaining operation of the RTC and a small SRAM,
referred to as the Battery RAM.
In Idle mode, execution of instructions is suspended until either a Reset or interrupt
occurs. Peripheral functions continue operation during Idle mode and may generate
interrupts to cause the processor to resume execution. Idle mode eliminates dynamic
power used by the processor itself, memory systems and related controllers, and internal
buses.
In Sleep mode, the oscillator is shut down and the chip receives no internal clocks. The
processor state and registers, peripheral registers, and internal SRAM values are
preserved throughout Sleep mode and the logic levels of chip pins remain static. The
output of the IRC is disabled but the IRC is not powered down for a fast wake-up later. The
32 kHz RTC oscillator is not stopped because the RTC interrupts may be used as the
wake-up source. The PLL is automatically turned off and disconnected. The CCLK and
USB clock dividers automatically get reset to zero.
The Sleep mode can be terminated and normal operation resumed by either a Reset or
certain specific interrupts that are able to function without clocks. Since all dynamic
operation of the chip is suspended, Sleep mode reduces chip power consumption to a
very low value. The flash memory is left on in Sleep mode, allowing a very quick wake-up.
On the wake-up from Sleep mode, if the IRC was used before entering Sleep mode, the
code execution and peripherals activities will resume after 4 cycles expire. If the main
external oscillator was used, the code execution will resume when 4096 cycles expire.
The customers need to reconfigure the PLL and clock dividers accordingly.
Power-down mode does everything that Sleep mode does, but also turns off the IRC
oscillator and the flash memory. This saves more power, but requires waiting for
resumption of flash operation before execution of code or data access in the flash memory
can be accomplished.
On the wake-up from Power-down mode, if the IRC was used before entering
Power-down mode, it will take IRC 60 s to start-up. After this 4 IRC cycles will expire
before the code execution can then be resumed if the code was running from SRAM. In
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 12 September 2011
Single-chip 16-bit/32-bit microcontroller
LPC2478
© NXP B.V. 2011. All rights reserved.
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