2003 Microchip Technology Inc.
DS39582B-page 127
PIC16F87XA
11.0
ANALOG-TO-DIGITAL
CONVERTER (A/D) MODULE
The Analog-to-Digital (A/D) Converter module has five
inputs for the 28-pin devices and eight for the 40/44-pin
devices.
The conversion of an analog input signal results in a
corresponding 10-bit digital number. The A/D module
has high and low-voltage reference input that is soft-
ware selectable to some combination of V
DD
, V
SS
, RA2
or RA3.
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.
The A/D module has four registers. These registers are:
• 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, con-
trols the operation of the A/D module. The ADCON1
register, shown in Register 11-2, configures the func-
tions of the port pins. The port pins can be configured
as analog inputs (RA3 can also be the voltage
reference) or as digital I/O.
Additional information on using the A/D module can be
found in the PICmicro
®
Mid-Range MCU Family
Reference Manual (DS33023).
REGISTER 11-1:
ADCON0 REGISTER (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 (ADCON0 bits in bold)
bit 5-3
CHS2:CHS0: Analog Channel Select bits
000
= Channel 0 (AN0)
001
= Channel 1 (AN1)
010
= Channel 2 (AN2)
011
= Channel 3 (AN3)
100
= Channel 4 (AN4)
101
= Channel 5 (AN5)
110
= Channel 6 (AN6)
111
= Channel 7 (AN7)
Note:
The PIC16F873A/876A devices only implement A/D channels 0 through 4; the
unimplemented selections are reserved. Do not select any unimplemented
channels with these devices.
bit 2
GO/DONE: A/D Conversion Status bit
When ADON =
1
:
1
= A/D conversion in progress (setting this bit starts the A/D conversion which is automatically
cleared by hardware when the A/D conversion is complete)
0
= A/D conversion not in progress
bit 1
Unimplemented: Read as ‘
0
’
bit 0
ADON: A/D On bit
1
= A/D converter module is powered up
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
ADCON1
<ADCS2>
ADCON0
<ADCS1:ADCS0>
Clock Conversion
0
00
F
OSC
/2
0
01
F
OSC
/8
0
10
F
OSC
/32
0
11
F
RC
(clock derived from the internal A/D RC oscillator)
1
00
F
OSC
/4
1
01
F
OSC
/16
1
10
F
OSC
/64
1
11
F
RC
(clock derived from the internal A/D RC oscillator)
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