Datasheet

 2001-2013 Microchip Technology Inc. DS39582C-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, 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
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 PIC
®
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)