PIC876 datasheet(113/218 Pages) MICROCHIP

113 / 218 page

 2001 Microchip Technology Inc.

DS30292C-page 111

PIC16F87X

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 other

devices.

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 dig-

ital result of this analog level via successive approxima-

tion. 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 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 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 Register0 (ADCON0)

• A/D Control Register1 (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 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).

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

= FOSC/2

= FOSC/8

= FOSC/32

= FRC (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, (RA5/AN4)

101

= channel 5, (RE0/AN5)(1)

110

= channel 6, (RE1/AN6)(1)

111

= channel 7, (RE2/AN7)(1)

bit 2

GO/DONE: A/D Conversion Status bit

If ADON = 1:

= A/D conversion in progress (setting this bit starts the A/D conversion)

= 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

= A/D converter module is operating

= A/D converter module is shut-off and consumes no operating current

Note 1: These channels are not available on PIC16F873/876 devices.

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

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