P89LPC901FD datasheet(38/55 Pages) PHILIPS

38 / 55 page

Philips Semiconductors

P89LPC901/902/903

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 04 — 21 November 2003

38 of 55

9397 750 12293

8.20 Internal reference voltage

An internal reference voltage generator may supply a default reference when a single

comparator input pin is used. The value of the internal reference voltage, referred to

as VREF, is 1.23 V ±10%.

8.21 Comparator interrupt

Each comparator has an interrupt ﬂag contained in its conﬁguration register. This ﬂag

is set whenever the comparator output changes state. The ﬂag may be polled by

software or may be used to generate an interrupt.

8.22 Comparator and power reduction modes

The comparators may remain enabled when Power-down or Idle mode is activated,

but the comparators are disabled automatically in Total Power-down mode.

If the comparator interrupt is enabled (except in Total Power-down mode), a change

of the comparator output state will generate an interrupt and wake up the processor. If

the comparator output to a pin is enabled, the pin should be conﬁgured in the

push-pull mode in order to obtain fast switching times while in Power-down mode.

The reason is that with the oscillator stopped, the temporary strong pull-up that

normally occurs during switching on a quasi-bidirectional port pin does not take

place.

The comparator consumes power in Power-down and Idle modes, as well as in the

normal operating mode. This fact should be taken into account when system power

consumption is an issue. To minimize power consumption, the user can disable the

comparator via PCONA.5 or put the device in Total Power-down mode.

Fig 19. Comparator input and output connections.

Comparator 1

CN1

(P0.4) CIN1A

(P0.5) CMPREF

VREF

OE1

Change Detect

CO1

CMF1

Interrupt

002aaa453

CMP1 (P0.6)

Change Detect

CMF2

Comparator 2

OE2

CO2

CMP2 (P0.0)

CN2

(P0.2) CIN2A

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