Datasheet

 2001-2013 Microchip Technology Inc. DS39598F-page 81
PIC16F818/819
11.0 ANALOG-TO-DIGITAL
CONVERTER (A/D) MODULE
The Analog-to-Digital (A/D) converter module has five
inputs for 18/20 pin devices.
The conversion of an analog input signal results in a
corresponding 10-bit digital number. The A/D module
has a high and low-voltage reference input that is
software selectable to some combination of V
DD, VSS,
RA2 or RA3.
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 A/D module has four registers:
• A/D Result High Register (ADRESH)
• A/D Result Low Register (ADRESL)
• A/D Control Register 0 (ADCON0)
• A/D Control Register 1 (ADCON1)
The ADCON0 register, shown in Register 11-1,
controls the operation of the A/D module. The
ADCON1 register, shown in Register 11-2, configures
the functions of the port pins. The port pins can be
configured as analog inputs (RA3 can also be a voltage
reference) or as digital I/Os.
Additional information on using the A/D module can be
found in the “PIC
®
Mid-Range MCU Family Reference
Manual” (DS33023).
REGISTER 11-1: ADCON0: A/D CONTROL REGISTER 0 (ADDRESS 1Fh)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 U-0 R/W-0
ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE
—ADON
bit 7 bit 0
bit 7-6 ADCS1:ADCS0: A/D Conversion Clock Select bits
If ADCS2 = 0:
00 = FOSC/2
01 = F
OSC/8
10 = F
OSC/32
11 = F
RC (clock derived from the internal A/D module RC oscillator)
If ADCS2 =
1:
00 = FOSC/4
01 = F
OSC/16
10 = F
OSC/64
11 = F
RC (clock derived from the internal A/D module RC oscillator)
bit 5-3 CHS2:CHS0: Analog Channel Select bits
000 = Channel 0 (RA0/AN0)
001 = Channel 1 (RA1/AN1)
010 = Channel 2 (RA2/AN2)
011 = Channel 3 (RA3/AN3)
100 = Channel 4 (RA4/AN4)
bit 2 GO/DONE
: A/D Conversion Status bit
If ADON =
1:
1 = A/D conversion in progress (setting this bit starts the A/D conversion)
0 = A/D conversion not in progress (this bit is automatically cleared by hardware when the
A/D conversion is complete)
bit 1 Unimplemented: Read as ‘0’
bit 0 ADON: A/D On bit
1 = A/D converter module is operating
0 = A/D converter module is shut-off and consumes no operating current
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown