PIC16F570 datasheet(61/134 Pages) MICROCHIP

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DS40001652C-page 61

PIC16F527

10.1

Comparator Operation

A single comparator is shown in Figure 10-2 along with

the relationship between the analog input levels and

the digital output. When the analog input at VIN+ is less

than the analog input VIN-, the output of the comparator

is a digital low level. The shaded area of the output of

the

comparator

Figure 10-2

represent

the

uncertainty due to input offsets and response time. See

Table 15-2 for Common Mode Voltage.

FIGURE 10-2:

SINGLE COMPARATOR

10.2

Comparator Reference

An internal reference signal may be used depending on

the comparator operating mode. The analog signal that

is present at VIN- is compared to the signal at VIN+, and

the digital output of the comparator is adjusted

accordingly

(see

Figure 10-2).

Please

see

Section 11.0

“Comparator

Voltage

Reference

Module” for internal reference specifications.

10.3

Comparator Response Time

Response time is the minimum time after selecting a

new reference voltage or input source before the

comparator output is to have a valid level. If the

comparator inputs are changed, a delay must be used

to allow the comparator to settle to its new state. Please

see Table 15-7 for comparator response time

specifications.

10.4

Comparator Output

The comparator output is read through the CxOUT bit

in the CM1CON0 or CM2CON0 register. This bit is

read-only. The comparator output may also be used

externally, see Section 10.1 “Comparator Opera-

tion”.

10.5

Comparator Wake-up Flag

The Comparator Wake-up Flag bit, CWIF, in the INT-

CON0 register, is set whenever all of the following con-

ditions are met:

•C1WU = 0 (CM1CON0<0>) or

C2WU = 0 (CM2CON0<0>)

• CM1CON0 or CM2CON0 has been read to latch

the last known state of the C1OUT and C2OUT bit

(MOVF CM1CON0, W)

• The output of a comparator has changed state

The wake-up flag may be cleared in software or by

another device Reset.

10.6

Comparator Operation During

Sleep

When the comparator is enabled it is active. To

minimize power consumption while in Sleep mode, turn

off the comparator before entering Sleep.

10.7

Effects of Reset

A Power-on Reset (POR) forces the CMxCON0

input pins to analog Reset mode. Device current is

minimized when analog inputs are present at Reset

time.

10.8

Analog Input Connection

Considerations

A simplified circuit for an analog input is shown in

Figure 10-3. Since the analog pins are connected to a

digital output, they have reverse biased diodes to VDD

and VSS. The analog input, therefore, must be between

VSS and VDD. If the input voltage deviates from this

range by more than 0.6V in either direction, one of the

diodes is forward biased and a latch-up may occur. A

maximum

source

impedance

10 k



recommended for the analog sources. Any external

component connected to an analog input pin, such as

a capacitor or a Zener diode, should have very little

leakage current.

–

VIN+

VIN-

Result

VIN-

VIN+

Note:

Analog levels on any pin that is defined as

a digital input may cause the input buffer

to consume more current than is speci-

fied.

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