P89LPC970FDH datasheet(28/66 Pages) NXP

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P89LPC97X_2

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Product data sheet

Rev. 02 — 27 April 2010

28 of 66

NXP Semiconductors

P89LPC970/971/972

8-bit microcontroller with accelerated two-clock 80C51 core

7.17.2 Power-on detection

The Power-on detect has a function similar to the brownout detect, but is designed to work

as power comes up initially to ensure that the device is reset from Power-on. The POF

flag in the RSTSRC register is set to indicate an initial power-up condition. The POF flag

will remain set until cleared by software.

7.17.3 Power reduction modes

The P89LPC970/971/972 supports three different power reduction modes. These modes

are Idle mode, Power-down mode, and total Power-down mode.

7.17.3.1

Idle mode

Idle mode leaves peripherals running in order to allow them to activate the processor

when an interrupt is generated. Any enabled interrupt source or reset may terminate Idle

mode.

7.17.3.2

Power-down mode

The Power-down mode stops the oscillator in order to minimize power consumption.

Brownout detection circuitry is disabled. The P89LPC970/971/972 exits Power-down

mode via any reset, or certain interrupts.

Some chip functions continue to operate and draw power during Power-down mode,

increasing the total power used during power-down. These include: Brownout detect,

watchdog timer, comparators and RTC/system timer (note that watchdog timer,

comparators and RTC/system timer can be powered down separately). The internal RC

oscillator is disabled unless both the RC oscillator has been selected as the system clock

and the RTC is enabled.

7.17.3.3

Total Power-down mode

The total Power-down mode is a deeper power reduction mode. Brownout detection

circuitry and analog comparators are disabled, as well as the internal RC oscillator.

Please use an external low frequency clock or 25 kHz watchdog oscillator to achieve low

power with the RTC running during power-down.

7.17.4 Regulators

Internal regulators can be adjusted automatically to minimize power consumption during

different power reduction modes. In Normal or Idle modes, power consumption can be

further reduced by configuring PMUCON register.

In Normal or Idle mode, regulators have two operation modes: High-speed mode and Low

current mode.

The regulators can be configured to Low current mode to reduce the power consumption.

After power-on-reset, internal regulators enter into High-speed mode as default.

PMUCON register is used to configure the regulators operation modes. LPMOD bit is

used to select the regulator’s mode and HCOK bit indicates whether the switch completed

or not. When switching back to high speed mode, first clear LPMOD bit to select high

speed mode, then check HCOK bit. If HCOK bit turns to ‘1’, it means the switch was

completed.

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