Datasheet

© 2007 Microchip Technology Inc. DS39629C-page 245
PIC18F6390/6490/8390/8490
19.9 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 19-4. 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 19-4: COMPARATOR ANALOG INPUT MODEL
TABLE 19-1: REGISTERS ASSOCIATED WITH 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
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 61
CVRCON CVREN CVROE CVRR
CVRSS CVR3 CVR2 CVR1 CVR0 61
INTCON GIE/GIEH PEIE/GIEL TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 59
PIR2
OSCFIF CMIF — — BCLIF HLVDIF TMR3IF CCP2IF 61
PIE2
OSCFIE CMIE — — BCLIE HLVDIE TMR3IE CCP2IE 61
IPR2 OSCFIP CMIP — — BCLIP HLVDIP TMR3IP CCP2IP 61
PORTF Read PORTF pins, Write LATF Latch 62
LATF LATF Data Output Register 62
TRISF PORTF Data Direction Register 62
Legend: — = unimplemented, read as ‘0’. Shaded cells are unused by the comparator module.