PIC18FXX20 Datasheet, PDF (218/366 Pages) Microchip Technology – 64/80-Pin High Performance 1 Mbit Enhanced FLASH Microcontrollers with A/D

PIC18FXX20
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.
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 volt-
age reference), or as a digital I/O. The ADRESH and
ADRESL registers contain the result of the A/D conver-
sion. When the A/D conversion is complete, the result
is loaded into the ADRESH/ADRESL registers, the
GO/DONE bit (ADCON0 register) is cleared, and 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
CHS3:CHS0
10-bit
Converter
A/D
VAIN
(Input Voltage)
Reference
Voltage
VCFG1:VCFG0
VREF+
VREF-
VDD
1111
1110
1101
1100
1011
1010
1001
1000
0111
0110
0101
0100
0011
0010
0001
0000
AN15⁽¹⁾
AN14⁽¹⁾
AN13⁽¹⁾
AN12⁽¹⁾
AN11
AN10
AN9
AN8
AN7
AN6
AN5
AN4
AN3
AN2
AN1
AN0
VSS
Note 1: Channels AN15 through AN12 are not available on PIC18F6X20 devices.
2: I/O pins have diode protection to VDD and VSS.
DS39609A-page 216
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 2003 Microchip Technology Inc.