Datasheet

© 2009 Microchip Technology Inc. DS39663F-page 275
PIC18F87J10 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
INTCON GIE/GIEH PEIE/GIEL
TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 53
PIR2
OSCFIF CMIF — — BCL1IF — TMR3IF CCP2IF 55
PIE2
OSCFIE CMIE — — BCL1IE — TMR3IE CCP2IE 55
IPR2
OSCFIP CMIP — — BCL1IP — TMR3IP CCP2IP 55
CMCON C2OUT C1OUT C2INV C1INV CIS CM2 CM1 CM0 55
CVRCON CVREN CVROE CVRR
CVRSS CVR3 CVR2 CVR1 CVR0 55
PORTF RF7 RF6 RF5 RF4 RF3 RF2 RF1 —56
LATF LATF7 LATF6 LATF5 LATF4 LATF3 LATF2 LATF1 —56
TRISF
TRISF7 TRISF6 TRISF5 TRISF4 TRISF3 TRISF2 TRISF1 —56
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
V
T = 0.6V
R
IC
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