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Philips Semiconductors
POWER MONITORING FUNCTIONS
Table 5-1: Brownout options
BOE
PMOD1-0
(UCFG1.5)
(PCON.1-0)
0 (erased)
XX
11
(total power
down)
≠ 11
1 (programmed)
(any mode
other than
total power
down)
Power-on Detection
The Power-On Detect has a function similar to the Brownout Detect, but is designed to work as power initially comes up, before
the power supply voltage reaches a level where the Brownout Detect can function. The POF flag (RSTSRC.4) is set to indicate
an initial power-on condition. The POF flag will remain set until cleared by software by writing '0' to the bit. Note that if BOE
(UCFG1.5) is programmed, BOF (RSTSRC.5) will be set when POF is set. If BOE is unprogrammed, BOF is meaningless.
Power reduction modes
The P89LPC920/921/922 supports three different power reduction modes as determined by SFR bits PCON.1-0 (see Table 5-2):
2003 Dec 8
BOPD
BOI
EBO
(PCON.5)
(PCON.4)
(IEN0.5)
X
X
X
X
1
(brownout
detect
X
powered
down)
0
(brownout
detect
generates
reset)
0
(brownout
(enable
detect
1
brownout
active)
(brownout
interrupt)
detect
generates
an
interrupt)
EA
(IEN0.7)
X
X
Brownout disabled. V
X
X
Brownout disabled. V
X
X
However, BOPD is default to '0' upon power-up.
Brownout reset enabled. V
3.6 V. Upon a brownout reset, BOF (RSTSRC.5) will be
X
X
set to indicate the reset source. BOF can be cleared by
writing '0' to the bit.
1
1
Brownout interrupt enabled. V
(global
3.6 V. Upon a brownout interrupt, BOF (RSTSRC.5) will
interrupt
be set. BOF can be cleared by writing '0' to the bit.
enable)
0
X
Both brownout reset and interrupt disabled. V
operating range is 2.4 V-3.6 V. However, BOF
(RSTSRC.5) will be set when V
X
0
Detection trip point. BOF can be cleared by writing '0' to
the bit.
34
User's Manual - Preliminary -
P89LPC920/921/922
Description
operating range is 2.4 V-3.6 V.
DD
operating range is 2.4 V-3.6 V.
DD
operating range is 2.7 V-
DD
operating range is 2.7 V-
DD
DD
falls to the Brownout
DD
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