PIC16F684-ESLASHST datasheet(69/164 Pages) MICROCHIP

69 / 164 page

 2004 Microchip Technology Inc.

Preliminary

DS41202C-page 67

PIC16F684

9.1.7

CONFIGURING THE A/D

After the A/D module has been configured as desired,

the selected channel must be acquired before the

conversion is started. The analog input channels must

have their corresponding TRIS bits selected as inputs.

To determine sample time, see Section 15.0 “Electri-

cal Specifications”. After this sample time has

elapsed, the A/D conversion can be started.

These steps should be followed for an A/D conversion:

Configure the A/D module:

• Configure analog/digital I/O (ANSEL)

• Configure voltage reference (ADCON0)

• Select A/D input channel (ADCON0)

• Select A/D conversion clock (ADCON1)

• Turn on A/D module (ADCON0)

Configure A/D interrupt (if desired):

• Clear ADIF bit (PIR1<6>)

• Set ADIE bit (PIE1<6>)

• Set PEIE and GIE bits (INTCON<7:6>)

Wait the required acquisition time.

Start conversion:

• Set GO/DONE bit (ADCON0<0>)

Wait for A/D conversion to complete, by either:

• Polling for the GO/DONE bit to be cleared

(with interrupts disabled); OR

• Waiting for the A/D interrupt

Read A/D Result register pair

(ADRESH:ADRESL), clear bit ADIF if required.

For next conversion, go to step 1 or step 2 as

required. The A/D conversion time per bit is

defined as TAD. A minimum wait of 2 TAD is

required before the next acquisition starts.

EXAMPLE 9-1:

A/D CONVERSION

;This code block configures the A/D

;for polling, Vdd reference, R/C clock

;and RA0 input.

;

;Conversion start & wait for complete

;polling code included.

;

BSF

STATUS,RP0

;Bank 1

MOVLW

B’01110000’

;A/D RC clock

MOVWF

ADCON1

BSF

TRISA,0

;Set RA0 to input

BSF

ANSEL,0

;Set RA0 to analog

BCF

STATUS,RP0

;Bank 0

MOVLW

B’10000001’

;Right, Vdd Vref, AN0

MOVWF

ADCON0

CALL

SampleTime

;Wait min sample time

BSF

ADCON0,GO

;Start conversion

BTFSC

ADCON0,GO

;Is conversion done?

GOTO

$-1

;No, test again

MOVF

ADRESH,W

;Read upper 2 bits

MOVWF

RESULTHI

BSF

STATUS,RP0

;Bank 1

MOVF

ADRESL,W

;Read lower 8 bits

MOVWF

RESULTLO

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