Datasheet

PIC18F2221/2321/4221/4321 FAMILY
DS39689F-page 244 © 2009 Microchip Technology Inc.
21.1 Comparator Configuration
There are eight modes of operation for the comparators,
shown in Figure 21-1. Bits CM<2:0> of the CMCON
register are used to select these modes. The TRISA reg-
ister 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 27.0
“Electrical Characteristics”.
FIGURE 21-1: 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
CM<2:0> = 000
C2
RA1/AN1
VIN-
V
IN+
RA2/AN2/
Off (Read as ‘0’)
A
A
C1
VIN-
V
IN+
C1OUT
Two Independent Comparators
A
A
CM<2:0> = 010
C2
VIN-
V
IN+
C2OUT
A
A
C1
VIN-
V
IN+
C1OUT
Two Common Reference Comparators
A
A
CM<2:0> = 100
C2
VIN-
V
IN+
C2OUT
A
D
C2
VIN-
V
IN+
Off (Read as ‘0’)
One Independent Comparator with Output
D
D
CM<2:0> = 001
C1
VIN-
V
IN+
C1OUT
A
A
C1
VIN-
V
IN+
Off (Read as ‘0’)
Comparators Off (POR Default Value)
D
D
CM<2:0> = 111
C2
VIN-
V
IN+
Off (Read as ‘0’)
D
D
C1
VIN-
V
IN+
C1OUT
Four Inputs Multiplexed to Two Comparators
A
A
CM<2:0> = 110
C2
VIN-
V
IN+
C2OUT
A
A
From VREF Module
CIS = 0
CIS = 1
CIS = 0
CIS = 1
C1
VIN-
V
IN+
C1OUT
Two Common Reference Comparators with Outputs
A
A
CM<2:0> = 101
C2
VIN-
V
IN+
C2OUT
A
D
A = Analog Input, port reads zeros always D = Digital Input CIS (CMCON<3>) is the Comparator Input Switch
CV
REF
C1
VIN-
V
IN+
C1OUT
Two Independent Comparators with Outputs
A
A
CM<2:0> = 011
C2
VIN-
V
IN+
C2OUT
A
A
RA5/AN4/SS/HLVDIN/C2OUT*
RA4/T0CKI/C1OUT*
VREF+
V
REF-/CVREF
RA0/AN0
RA3/AN3/
RA1/AN1
RA2/AN2/
V
REF+
V
REF-/CVREF
RA0/AN0
RA3/AN3/
RA1/AN1
RA2/AN2/
V
REF+
V
REF-/CVREF
RA0/AN0
RA3/AN3/
RA1/AN1
RA2/AN2/
V
REF+
V
REF-/CVREF
RA0/AN0
RA3/AN3/
RA1/AN1
RA2/AN2/
V
REF+
V
REF-/CVREF
RA0/AN0
RA3/AN3/
RA1/AN1
RA2/AN2/
V
REF+
V
REF-/CVREF
RA0/AN0
RA3/AN3/
V
REF+
RA1/AN1
RA2/AN2/
V
REF-/CVREF
RA4/T0CKI/C1OUT*
RA5/AN4/SS
/HLVDIN/C2OUT*
RA0/AN0
RA3/AN3/
V
REF+
RA1/AN1
RA2/AN2/
V
REF-/CVREF
RA4/T0CKI/C1OUT*
* Setting the TRISA<5:4> bits will disable the comparator outputs by configuring the pins as inputs.