Datasheet

 2010 Microchip Technology Inc. Preliminary DS39979A-page 297
PIC18F87J72 FAMILY
23.9 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 23-4. 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 k 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 23-4: COMPARATOR ANALOG INPUT MODEL
TABLE 23-1: 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 49
PIR2 OSCFIF CMIF — — BCLIF LVDIF TMR3IF —52
PIE2
OSCFIE CMIE — — BCLIE LVDIE TMR3IE —52
IPR2 OSCFIP CMIP — — BCLIP LVDIP TMR3IP —52
CMCON C2OUT C1OUT C2INV C1INV CIS CM2 CM1 CM0 51
CVRCON CVREN CVROE CVRR
CVRSS CVR3 CVR2 CVR1 CVR0 51
PORTF RF7 RF6 RF5 RF4 RF3 RF2 RF1 —52
LATF LATF7 LATF6 LATF5 LATF4 LATF3 LATF2 LATF1 —52
TRISF
TRISF7 TRISF6 TRISF5 TRISF4 TRISF3 TRISF2 TRISF1 —52
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
±100 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