PIC18FXX8 Datasheet, PDF (245/402 Pages) Microchip Technology – 28/40-Pin High-Performance, Enhanced Flash Microcontrollers with CAN Module

PIC18FXX8
The analog reference voltage is software selectable to
either the device’s positive and negative supply voltage
(VDD and VSS) or the voltage level on the RA3/AN3/
VREF+ pin and RA2/AN2/VREF- pin.
The A/D converter has a unique feature of being able
to operate while the device is in Sleep mode. To oper-
ate in Sleep, the A/D conversion clock must be derived
from the A/D’s internal RC oscillator.
The output of the sample and hold is the input into the
converter which generates the result via successive
approximation.
FIGURE 20-1:
A/D BLOCK DIAGRAM
A device Reset forces all registers to their Reset state.
This forces the A/D module to be turned off and any
conversion is aborted.
Each port pin associated with the A/D converter can be
configured as an analog input (RA3 can also be a
voltage reference) or as a digital I/O.
The ADRESH and ADRESL registers contain the result
of the A/D conversion. When the A/D conversion is com-
plete, the result is loaded into the ADRESH/ADRESL
registers, the GO/DONE bit (ADCON0<2>) is cleared
and A/D Interrupt Flag bit, ADIF, is set. The block
diagram of the A/D module is shown in Figure 20-1.
CHS2:CHS0
10-bit
Converter
A/D
Reference
voltage
VAIN
(Input Voltage)
VREF+
PCFG0
VDD
VREF-
111
AN7⁽¹⁾
110
AN6⁽¹⁾
101
AN5⁽¹⁾
100
AN4
011
AN3
010
AN2
001
AN1
000
AN0
VSS
Note 1: Channels AN5 through AN7 are not available on PIC18F2X8 devices.
2: All I/O pins have diode protection to VDD and VSS.
 2004 Microchip Technology Inc.
DS41159D-page 243