PIC16F877ATISLASHML datasheet(129/234 Pages) MICROCHIP

129 / 234 page

 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 VDD, 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

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).

ADCON0 REGISTER (ADDRESS 1Fh)

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:

= 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)

= A/D conversion not in progress

bit 1

Unimplemented: Read as ‘0’

bit 0

ADON: A/D On bit

= A/D converter module is powered up

= 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

FOSC/2

FOSC/8

FOSC/32

FRC (clock derived from the internal A/D RC oscillator)

FOSC/4

FOSC/16

FOSC/64

FRC (clock derived from the internal A/D RC oscillator)

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