Datasheet

PIC16F87/88
DS30487D-page 122  2002-2013 Microchip Technology Inc.
13.1 Comparator Configuration
There are eight modes of operation for the compara-
tors. The CMCON register is used to select these
modes. Figure 13-1 shows the eight possible modes.
The TRISA register controls the data direction of the
comparator pins for each mode. If the Comparator
mode is changed, the comparator output level may not
be valid for the specified mode change delay shown in
Section 18.0 “Electrical Characteristics”.
FIGURE 13-1: COMPARATOR I/O OPERATING MODES
Note: Comparator interrupts should be disabled
during a Comparator mode change;
otherwise, a false interrupt may occur.
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
Off (Read as ‘0’)
Comparators Reset
A
A
CM2:CM0 = 000
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
Off
(Read as ‘0’)
A
A
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
C1OUT
Two Independent Comparators
A
A
CM2:CM0 = 100
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
C2OUT
A
A
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
C1OUT
Two Common Reference Comparators
A
D
CM2:CM0 = 011
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
C2OUT
A
A
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
Off
(Read as ‘0’)
One Independent Comparator
D
D
CM2:CM0 = 101
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
C2OUT
A
A
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
Off
(Read as ‘0’)
Comparators Off (POR Default Value)
D
D
CM2:CM0 = 111
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
Off
(Read as ‘0’)
D
D
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
C1OUT
Four Inputs Multiplexed to Two Comparators
A
A
CM2:CM0 = 010
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
C2OUT
A
A
From VREF Module
CIS = 0
CIS = 1
CIS = 0
CIS = 1
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
C1OUT
Two Common Reference Comparators with Outputs
A
D
CM2:CM0 = 110
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
C2OUT
A
A
A = Analog Input, port reads zeros always.
D = Digital Input.
CIS (CMCON<3>) is the Comparator Input Switch.
RA4/T0CKI/C2OUT
C1
RA0/AN0
VIN-
V
IN+
RA3/AN3/
C1OUT
Three Inputs Multiplexed to Two Comparators
A
A
CM2:CM0 = 001
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
C2OUT
A
A
CIS = 0
CIS = 1
C1OUT
C1OUT
C1OUT
C1OUT C1OUT
C1OUT
C1OUT
C1OUT
CV
REF
CVREF
CVREF
CVREF
CVREF
CVREF
CVREF
CVREF