Datasheet

PIC18F6390/6490/8390/8490
DS39629C-page 234 © 2007 Microchip Technology Inc.
The analog reference voltage is software selectable to
either the device’s positive and negative supply voltage
(AVDD and AVSS), or the voltage level on the
RA3/AN3/V
REF+/SEG17 and RA2/AN2/VREF-/SEG16
pins.
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.
A device Reset forces all registers to their Reset state.
This forces the A/D module to be turned off and any
conversion in progress is aborted.
Each port pin associated with the A/D converter can be
configured as an analog input 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<1>) is cleared
and the A/D Interrupt Flag bit, ADIF, is set. The block
diagram of the A/D module is shown in Figure 18-1.
FIGURE 18-1: A/D BLOCK DIAGRAM
(Input Voltage)
VAIN
VREF+
Reference
Voltage
AV
DD
(1)
VCFG1:VCFG0
CHS3:CHS0
AN7
AN6
AN5
AN4
AN3
AN2
AN1
AN0
0111
0110
0101
0100
0011
0010
0001
0000
10-Bit
A/D
VREF-
AVSS
(1)
Converter
AN11
AN10
AN9
AN8
1011
1010
1001
1000
Note 1: I/O pins have diode protection to VDD and VSS.
0X
1X
X
1
X0