PIC18F2420/2520/4420/4520
The analog reference voltage is software selectable to
either the device’s positive and negative supply voltage
(V
DD
and V
SS
), or the voltage level on the RA3/AN3/
V
REF
+ and RA2/AN2/V
REF
-/CV
REF
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 complete,
the result is loaded into the ADRESH:ADRESL register
pair, the GO/DONE bit (ADCON0 register) is cleared and
the A/D Interrupt Flag bit, ADIF, is set. The block diagram
of the A/D module is shown in Figure 19-1.
FIGURE 19-1:
A/D BLOCK DIAGRAM
CHS<3:0>
1100
1011
1010
1001
1000
0111
0110
0101
0100
V
AIN
AN12
AN11
AN10
AN9
AN8
AN7
(1)
AN6
(1)
AN5
(1)
AN4
AN3
AN2
AN1
AN0
10-Bit
A/D
Converter
(Input Voltage)
0011
0010
VCFG<1:0>
V
DD
(2)
Reference
Voltage
V
REF
+
V
REF
-
X
0
X
1
1
X
0001
0000
0
X
V
SS
(2)
Note 1:
2:
Channels, AN5 through AN7, are not available on 28-pin devices.
I/O pins have diode protection to V
DD
and V
SS
.
DS39631E-page 226
©
2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
