PIC16F870/871
The A/D module has four registers. These registers
are:
10.0 ANALOG-TO-DIGITAL
CONVERTER (A/D) MODULE
The Analog-to-Digital (A/D) Converter module has five
inputs for the PIC16F870 and eight for the PIC16F871.
• A/D Result High Register (ADRESH)
• A/D Result Low Register (ADRESL)
• A/D Control Register0 (ADCON0)
• A/D Control Register1 (ADCON1)
The analog input charges a sample and hold capacitor.
The output of the sample and hold capacitor is the
input into the converter. The converter then generates
a digital result of this analog level via successive
approximation. The A/D conversion of the analog input
signal results in a corresponding 10-bit digital number.
The A/D module has high and low voltage reference
input that is software selectable to some combination
of VDD, VSS, RA2 or RA3.
The ADCON0 register, shown in Register 10-1, con-
trols the operation of the A/D module. The ADCON1
register, shown in Register 10-2, configures the func-
tions of the port pins. The port pins can be configured
as analog inputs (RA3 can also be the voltage refer-
ence) or as digital I/O.
Additional information on using the A/D module can be
found in the PICmicro™ Mid-Range MCU Family Ref-
erence Manual (DS33023).
The A/D converter has a unique feature of being able to
operate while the device is in SLEEP mode. To operate
in sleep, the A/D clock must be derived from the A/D’s
internal RC oscillator.
REGISTER 10-1: ADCON0 REGISTER (ADDRESS: 1Fh)
R/W-0
R/W-0
R/W-0
CHS2
R/W-0
CHS1
R/W-0
CHS0
R/W-0
U-0
R/W-0
ADON
bit0
ADCS1 ADCS0
GO/DONE
—
R = Readable bit
W = Writable bit
U = Unimplemented bit,
read as ‘0’
bit7
- n = Value at POR reset
bit 7-6: ADCS1:ADCS0: A/D Conversion Clock Select bits
00= FOSC/2
01= FOSC/8
10= FOSC/32
11= FRC (clock derived from an RC oscillation)
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, (RA5/AN4)
101= channel 5, (RE0/AN5)
110= channel 6, (RE1/AN6)
111= channel 7, (RE2/AN7)
(1)
(1)
(1)
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:
bit 0:
Unimplemented: Read as '0'
ADON: A/D On bit
1= A/D converter module is operating
0= A/D converter module is shutoff and consumes no operating current
Note 1: These channels are not available on the PIC16F870.
1999 Microchip Technology Inc.
Preliminary
DS30569A-page 79
MICROCHIP [ MICROCHIP ]
