
PIC16F87XA
DS39582A-page 134
Advance Information
2001 Microchip Technology Inc.
12.1
Comparator Configuration
There are eight modes of operation for the compara-
tors. The CMCON register is used to select these
modes. Figure 12-1 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
the Electrical Specifications (Section 17.0).
FIGURE 12-1:
Comparators Reset (POR Default Value)
CM2:CM0 =
000
COMPARATOR I/O OPERATING MODES
Note:
Comparator interrupts should be disabled
during a Comparator mode change. Other-
wise, a false interrupt may occur.
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
Off
(Read as ’0’)
A
A
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
Off
(Read as ’0’)
A
A
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
C1OUT
Two Independent Comparators
CM2:CM0 =
010
A
A
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
C2OUT
A
A
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
C1OUT
Two Common Reference Comparators
CM2:CM0 =
100
A
A
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
C2OUT
A
D
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
Off
(Read as ’0’)
One Independent Comparator with Output
CM2:CM0 =
001
D
D
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
C1OUT
A
A
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
Off
(Read as ’0’)
Comparators Off
CM2:CM0 =
111
D
D
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
Off
(Read as ’0’)
D
D
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
C1OUT
Four Inputs Multiplexed to Two Comparators
CM2:CM0 =
110
A
A
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
C2OUT
A
A
From Comparator
V
REF
Module
CIS =
0
CIS =
1
CIS =
0
CIS =
1
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
C1OUT
Two Common Reference Comparators with Outputs
CM2:CM0 =
101
A
A
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
C2OUT
A
D
A = Analog Input, port reads zeros always. D = Digital Input. CIS (CMCON<3>) is the Comparator Input Switch.
CV
REF
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
C1OUT
Two Independent Comparators with Outputs
CM2:CM0 =
011
A
A
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
C2OUT
A
A
RA4/T0CKI/C1OUT
RA5/SS/AN4/C2OUT
RA4/T0CKI/C1OUT
RA5/SS/AN4/C2OUT
RA4/T0CKI/C1OUT