Microchip Technology DV164136 Data Sheet
© 2008 Microchip Technology Inc.
DS39646C-page 285
PIC18F8722 FAMILY
22.9
Analog Input Connection
Considerations
Considerations
A simplified circuit for an analog input is shown in
Figure 22-4. Since the analog pins are connected to a
digital output, they have reverse biased diodes to V
Figure 22-4. Since the analog pins are connected to a
digital output, they have reverse biased diodes to V
DD
and V
SS
. The analog input, therefore, must be between
V
SS
and V
DD
. If the input voltage deviates from this
range by more than 0.6V in either direction, one of the
diodes is forward biased and a latch-up condition may
occur. A maximum source impedance of 10 k
diodes is forward biased and a latch-up condition may
occur. A maximum source impedance of 10 k
Ω is
recommended for the analog sources. Any external
component connected to an analog input pin, such as
a capacitor or a Zener diode, should have very little
leakage current.
component connected to an analog input pin, such as
a capacitor or a Zener diode, should have very little
leakage current.
FIGURE 22-4:
COMPARATOR ANALOG INPUT MODEL
TABLE 22-1:
REGISTERS ASSOCIATED WITH COMPARATOR MODULE
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset
Values
on page
CMCON
C2OUT
C1OUT
C2INV
C1INV
CIS
CM2
CM1
CM0
CVRCON
CVREN
CVROE
CVRR
CVRSS
CVR3
CVR2
CVR1
CVR0
INTCON
GIE/GIEH PEIE/GIEL
TMR0IE
INT0IE
RBIE
TMR0IF
INT0IF
RBIF
PIR2
OSCFIF
CMIF
—
EEIF
BCL1IF
HLVDIF
TMR3IF
CCP2IF
PIE2
OSCFIE
CMIE
—
EEIE
BCL1IE
HLVDIE
TMR3IE
CCP2IE
IPR2
OSCFIP
CMIP
—
EEIP
BCL1IP
HLVDIP
TMR3IP
CCP2IP
TRISF
TRISF7
TRISF6
TRISF5
TRISF4
TRISF3
TRISF2
TRISF1
TRISF0
Legend: — = unimplemented, read as ‘0’. Shaded cells are unused by the comparator module.
VA
R
S
< 10k
A
IN
C
PIN
5 pF
V
DD
V
T
= 0.6V
V
T
= 0.6V
R
IC
I
LEAKAGE
±500 nA
V
SS
Legend:
C
PIN
= Input Capacitance
V
T
= Threshold
Voltage
I
LEAKAGE
= Leakage Current at the pin due to various junctions
R
IC
= Interconnect Resistance
R
S
= Source
Impedance
VA
= Analog
Voltage
Comparator
Input
Input