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.
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).
EXAMPLE 9-1: INITIALIZING
COMPARATOR MODULE
FIGURE 9-2: SINGLE COMPARATOR
FLAG_REG EQU
0X20
CLRF
CLRF
FLAG_REG
PORTA
;Init flag register
;Init PORTA
MOVF
CMCON, W
0xC0
;Load comparator bits
;Mask comparator bits
VIN+
+
–
ANDLW
IORWF
MOVLW
MOVWF
BSF
Output
FLAG_REG,F ;Store bits in flag register
0x03
CMCON
VIN–
;Init comparator mode
;CM<2:0> = 011
STATUS,RP0 ;Select Bank1
MOVLW
MOVWF
0x07
TRISA
;Initialize data direction
;Set RA<2:0> as inputs
;RA<4:3> as outputs
V
IN–
IN+
;TRISA<7:5> always read ‘0’
STATUS,RP0 ;Select Bank 0
BCF
CALL
MOVF
BCF
BSF
BSF
BCF
BSF
BSF
DELAY 10
CMCON,F
PIR1,CMIF
;10µs delay
;Read CMCONtoendchangecondition
;Clear pending interrupts
V
STATUS,RP0 ;Select Bank 1
PIE1,CMIE
;Enable comparator interrupts
STATUS,RP0 ;Select Bank 0
INTCON,PEIE ;Enable peripheral interrupts
INTCON,GIE ;Global interrupt enable
Output
9.2
Comparator Operation
9.3.1
EXTERNAL REFERENCE SIGNAL
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.
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
is used when the comparators are in mode
CM<2:0>=010 (Figure 9-1). In this mode, the internal
voltage reference is applied to the VIN+ pin of both
comparators.
1999 Microchip Technology Inc.
Preliminary
DS40300B-page 59
MICROCHIP [ MICROCHIP ]
