P89LPC913 datasheet(43/63 Pages) PHILIPS

43 / 63 page

Philips Semiconductors

P89LPC912/913/914

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 03 — 17 December 2004

43 of 63

9397 750 14468

9.19 Analog comparators

Two analog comparators are provided on the P89LPC912/913/914. Input and output

options allow use of the comparators in a number of different conﬁgurations.

Comparator operation is such that the output is a logical ‘1’ when the positive input is

greater than the negative input (selectable from a pin or an internal reference

voltage). Otherwise the output is a zero. Each comparator may be conﬁgured to

cause an interrupt when the output value changes. Comparator 1 may be output to a

port pin.

The overall connections to both comparators are shown in Figure 21. The

comparators function to VDD = 2.4 V.

When each comparator is ﬁrst enabled, the comparator output and interrupt ﬂag are

not guaranteed to be stable for 10 microseconds. The corresponding comparator

interrupt should not be enabled during that time, and the comparator interrupt ﬂag

must be cleared before the interrupt is enabled in order to prevent an immediate

interrupt service.

9.20 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 %.

9.21 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. The two comparators use one

common interrupt vector. If both comparators enable interrupts, after entering the

interrupt service routine, the user needs to read the ﬂags to determine which

comparator caused the interrupt.

Possible comparator conﬁgurations are shown in Figure 22.

Fig 21. Comparator input and output connections.

Comparator 1

CN1

(P0.4) CIN1A

(P0.5) CMPREF

VREF

OE1

Change Detect

CO1

CMF1

Interrupt

002aaa496

CMP1 (P0.6)

Change Detect

CMF2

Comparator 2

CN2

(P0.2) CIN2A

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