PIC18F2420/2520/4420/4520
20.0
COMPARATOR MODULE
The analog comparator module contains two
comparators that can be configured in a variety of
ways. The inputs can be selected from the analog
inputs multiplexed with pins, RA0 through RA5, as well
as the on-chip voltage reference (see
The digi-
tal outputs (normal or inverted) are available at the pin
level and can also be read through the control register.
The CMCON register (Register 20-1) selects the
comparator input and output configuration. Block
diagrams of the various comparator configurations are
shown in Figure 20-1.
REGISTER 20-1:
R-0
C2OUT
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7
CMCON: COMPARATOR CONTROL REGISTER
R-0
R/W-0
C2INV
R/W-0
C1INV
R/W-0
CIS
R/W-1
CM2
R/W-1
CM1
R/W-1
CM0
bit 0
C1OUT
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
C2OUT:
Comparator 2 Output bit
When C2INV =
0:
1
= C2 V
IN
+ > C2 V
IN
-
0
= C2 V
IN
+ < C2 V
IN
-
When C2INV =
1:
1
= C2 V
IN
+ < C2 V
IN
-
0
= C2 V
IN
+ > C2 V
IN
-
C1OUT:
Comparator 1 Output bit
When C1INV =
0:
1
= C1 V
IN
+ > C1 V
IN
-
0
= C1 V
IN
+ < C1 V
IN
-
When C1INV =
1:
1
= C1 V
IN
+ < C1 V
IN
-
0
= C1 V
IN
+ > C1 V
IN
-
C2INV:
Comparator 2 Output Inversion bit
1
= C2 output inverted
0
= C2 output not inverted
C1INV:
Comparator 1 Output Inversion bit
1
= C1 output inverted
0
= C1 output not inverted
CIS:
Comparator Input Switch bit
When CM<2:0> =
110:
1
= C1 V
IN
- connects to RA3/AN3/V
REF
+
C2 V
IN
- connects to RA2/AN2/V
REF
-/CV
REF
0
= C1 V
IN
- connects to RA0/AN0
C2 V
IN
- connects to RA1/AN1
CM<2:0>:
Comparator Mode bits
bit 6
bit 5
bit 4
bit 3
bit 2-0
©
2008 Microchip Technology Inc.
DS39631E-page 233
MICROCHIP [ MICROCHIP TECHNOLOGY ]
