P87LPC778FDH datasheet(19/79 Pages) PHILIPS

19 / 79 page

Philips Semiconductors

P87LPC778

CMOS single-chip 8-bit microcontroller

Product data

Rev. 01 — 31 March 2004

19 of 79

9397 750 12378

8.5.2

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 1.28 V

±10 %.

8.5.3

Comparator interrupt

Each comparator has an interrupt ﬂag CMFn 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. The interrupt will be

generated when the corresponding enable bit ECn in the IEN1 register is set and the

interrupt system is enabled via the EA bit in the IEN0 register.

8.5.4

Comparators and power reduction modes

Either or both comparators may remain enabled when Power-down or Idle mode is

activated. The comparators will continue to function in the power reduction mode. If a

comparator interrupt is enabled, 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.

Comparators consume 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.

CPn, CNn, OEn=000

CPn, CNn, OEn=001

CPn, CNn, OEn=010

CPn, CNn, OEn=011

CPn, CNn, OEn=100

CPn, CNn, OEn=101

CPn, CNn, OEn=110

CPn, CNn, OEn=111

Fig 7.

Comparator conﬁgurations.

CINnA

CMPREF

002aaa618

COn

CINnA

CMPREF

002aaa620

COn

CMPn

CINnA

VREF (1.23V)

002aaa621

COn

CINnA

VREF (1.23 V)

002aaa622

COn

CMPn

CINnB

CMPREF

002aaa623

COn

CINnB

CMPREF

002aaa624

COn

CMPn

CINnB

VREF (1.23V)

002aaa625

COn

CINnB

VREF (1.23 V)

002aaa626

COn

CMPn

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