P89LPC9321 datasheet(29/70 Pages) NXP

29 / 70 page

P89LPC9321_1

Product data sheet

Rev. 01 — 9 December 2008

29 of 70

NXP Semiconductors

P89LPC9321

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

7.17.1 Brownout detection

The brownout detect function determines if the power supply voltage drops below a

certain level. Enhanced brownout detection has 3 independent functions: BOD reset,

BOD interrupt and BOD EEPROM/FLASH.

BOD reset is always on except in total power-down mode. It could not be disabled in

software. BOD interrupt may be enabled or disabled in software. BOD EEPROM/FLASH is

always on, except in power-down modes and could not be disabled in software.

BOD reset and BOD interrupt, each has four trip voltage levels. BOE1 bit (UCFG1.5) and

BOE0 bit (UCFG1.3) are used as trip point conﬁguration bits of BOD reset. BOICFG1 bit

and BOICFG0 bit in register BODCFG are used as trip point conﬁguration bits of BOD

interrupt. BOD reset voltage should be lower than BOD interrupt trip point. BOD

EEPROM/FLASH is used for ﬂash/Data EEPROM programming/erase protection and has

only 1 trip voltage of 2.4 V. Please refer to P89LPC9321

User manual for detail

conﬁgurations.

If brownout detection is enabled the brownout condition occurs when VDD falls below the

brownout trip voltage and is negated when VDD rises above the brownout trip voltage.

For correct activation of brownout detect, the VDD rise and fall times must be observed.

Please see Table 10 “Static characteristics” for speciﬁcations.

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, before the power supply voltage reaches a level where

brownout detect can work. 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.

7.18 Power reduction modes

The P89LPC9321 supports three different power reduction modes. These modes are Idle

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

7.18.1 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.

7.18.2 Power-down mode

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

P89LPC9321 exits Power-down mode via any reset, or certain interrupts. In Power-down

mode, the power supply voltage may be reduced to the data retention supply voltage

VDDR. This retains the RAM contents at the point where Power-down mode was entered.

SFR contents are not guaranteed after VDD has been lowered to VDDR, therefore it is

highly recommended to wake-up the processor via reset in this case. VDD must be raised

to within the operating range before the Power-down mode is exited.

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