PIC18F2682 Datasheet, PDF (263/484 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology

PIC18F2682/2685/4682/4685
20.9 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 20-4. 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
VSS 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 20-4:
COMPARATOR ANALOG INPUT MODEL
VDD
RS < 10k
AIN
VA
CPIN
5 pF
VT = 0.6V
VT = 0.6V
RIC
ILEAKAGE
±500 nA
Comparator
Input
VSS
Legend:
CPIN
=
VT
=
ILEAKAGE =
RIC
=
RS
=
VA
=
Input Capacitance
Threshold Voltage
Leakage Current at the pin due to various junctions
Interconnect Resistance
Source Impedance
Analog Voltage
TABLE 20-1: 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⁽³⁾ C2OUT C1OUT C2INV C1INV
CIS
CM2
CM1
CM0
51
CVRCON⁽³⁾ CVREN CVROE CVRR CVRSS CVR3 CVR2 CVR1
CVR0
51
INTCON GIE/GIEH PEIE/GIEL TMR0IE INT0IE RBIE TMR0IF INT0IF
RBIF
52
IPR2
OSCFIP CMIP⁽²⁾
—
EEIP BCLIP HLVDIP TMR3IP ECCP1IP⁽²⁾ 51
PIR2
OSCFIF CMIF⁽²⁾
—
EEIF BCLIF HLVDIF TMR3IF ECCP1IF⁽²⁾ 52
PIE2
OSCFIE CMIE⁽²⁾
—
EEIE BCLIE HLVDIE TMR3IE ECCP1IE⁽²⁾ 52
PORTA
RA7⁽¹⁾
RA6⁽¹⁾
RA5
RA4
RA3
RA2
RA1
RA0
52
LATA
LATA7⁽¹⁾ LATA6⁽¹⁾ LATA Data Output Register
52
TRISA
TRISA7⁽¹⁾ TRISA6⁽¹⁾ PORTA Data Direction Register
52
Legend: — = unimplemented, read as ‘0’. Shaded cells are unused by the comparator module.
Note 1: PORTA pins are enabled based on oscillator configuration.
2: These bits are available in PIC18F4682/4685 devices and reserved in PIC18F2682/2685 devices.
3: These registers are unimplemented on PIC18F2682/2685 devices.
© 2007 Microchip Technology Inc.
Preliminary
DS39761B-page 261