Datasheet

© 2008 Microchip Technology Inc. DS39646C-page 285
PIC18F8722 FAMILY
22.9 Analog Input Connection
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 VDD
and VSS. The analog input, therefore, must be between
V
SS and VDD. 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 kΩ 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.
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 59
CVRCON CVREN CVROE CVRR
CVRSS CVR3 CVR2 CVR1 CVR0 59
INTCON GIE/GIEH PEIE/GIEL
TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 60
PIR2
OSCFIF CMIF — EEIF BCL1IF HLVDIF TMR3IF CCP2IF 60
PIE2 OSCFIE CMIE — EEIE BCL1IE HLVDIE TMR3IE CCP2IE 60
IPR2
OSCFIP CMIP — EEIP BCL1IP HLVDIP TMR3IP CCP2IP 60
TRISF TRISF7 TRISF6 TRISF5 TRISF4TRISF3TRISF2TRISF1TRISF0 60
Legend: — = unimplemented, read as ‘0’. Shaded cells are unused by the comparator module.
VA
R
S < 10k
A
IN
CPIN
5 pF
V
DD
VT = 0.6V
VT = 0.6V
RIC
ILEAKAGE
±500 nA
V
SS
Legend: CPIN = 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