PIC16F87XA
DS39582B-page 136
2003 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
Section 17.0 “Electrical Characteristics”.
FIGURE 12-1:
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
V
IN
-
V
IN
+
RA3/AN3
Off (Read as ‘
0
’)
Comparators Reset
A
A
CM2:CM0 =
000
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
A
A
CM2:CM0 =
010
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
A
A
CM2:CM0 =
100
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
D
D
CM2:CM0 =
001
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 (POR Default Value)
D
D
CM2:CM0 =
111
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
A
A
CM2:CM0 =
110
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
C2OUT
A
A
From Comparator
CIS =
0
CIS =
1
CIS =
0
CIS =
1
C1
RA0/AN0
V
IN
-
V
IN
+
RA3/AN3
C1OUT
Two Common Reference Comparators with Outputs
A
A
CM2:CM0 =
101
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
A
A
CM2:CM0 =
011
C2
RA1/AN1
V
IN
-
V
IN
+
RA2/AN2
C2OUT
A
A
RA4/T0CKI/C1OUT
RA5/AN4/SS/C2OUT
RA4/T0CKI/C1OUT
RA5/AN4/SS/C2OUT
RA4/T0CKI/C1OUT
V
REF
Module
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