PIC16F628-20SLASHSS datasheet(59/160 Pages) MICROCHIP

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Preliminary

DS40300B-page 59

PIC16F62X

The code example in Example 9-1 depicts the steps

required to configure the comparator module. RA3 and

RA4 are configured as digital output. RA0 and RA1 are

configured as the V- inputs and RA2 as the V+ input to

both comparators.

EXAMPLE 9-1:

INITIALIZING

COMPARATOR MODULE

9.2

Comparator Operation

A single comparator is shown in Figure 9-2 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. When the analog input

at VIN+ is greater than the analog input VIN–, the output

of the comparator is a digital high level. The shaded

areas of the output of the comparator in Figure 9-2

represent the uncertainty due to input offsets and

response time.

FLAG_REG

EQU

0X20

CLRF

FLAG_REG

;Init flag register

CLRF

PORTA

;Init PORTA

MOVF

CMCON, W

;Load comparator bits

ANDLW

0xC0

;Mask comparator bits

IORWF

FLAG_REG,F

;Store bits in flag register

MOVLW

0x03

;Init comparator mode

MOVWF

CMCON

;CM<2:0> = 011

BSF

STATUS,RP0

;Select Bank1

MOVLW

0x07

;Initialize data direction

MOVWF

TRISA

;Set RA<2:0> as inputs

;RA<4:3> as outputs

;TRISA<7:5> always read ‘0’

BCF

STATUS,RP0

;Select Bank 0

CALL

DELAY 10

;10

µs delay

MOVF

CMCON,F

;Read CMCONtoend change condition

BCF

PIR1,CMIF

;Clear pending interrupts

BSF

STATUS,RP0

;Select Bank 1

BSF

PIE1,CMIE

;Enable comparator interrupts

BCF

STATUS,RP0

;Select Bank 0

BSF

INTCON,PEIE

;Enable peripheral interrupts

BSF

INTCON,GIE

;Global interrupt enable

9.3

Comparator Reference

An external or 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 (Figure 9-2).

FIGURE 9-2:

SINGLE COMPARATOR

9.3.1

EXTERNAL REFERENCE SIGNAL

When external voltage references are used, the

comparator module can be configured to have the com-

parators operate from the same or different reference

sources. However, threshold detector applications may

require the same reference. The reference signal must

be between VSS and VDD, and can be applied to either

pin of the comparator(s).

9.3.2

INTERNAL REFERENCE SIGNAL

The comparator module also allows the selection of an

internally

generated

voltage

reference

for

the

comparators. Section 13, Instruction Sets, contains a

detailed description of the Voltage Reference Module

that provides this signal. The internal reference signal

used

when

the

comparators

are

mode

CM<2:0>=010 (Figure 9-1). In this mode, the internal

voltage reference is applied to the VIN+ pin of both

comparators.

–

VIN+

VIN–

Output

VIN–

VIN+

Output

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