OPTION_REG datasheet(126/222 Pages) MICROCHIP

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MCP19111

DS22331A-page 126

 2013 Microchip Technology Inc.

22.2

ADC Operation

22.2.1

STARTING A CONVERSION

To enable the ADC module, the ADON bit of the

ADCON0 register must be set to a ‘1’. Setting the

GO/DONE bit of the ADCON0 register to a ‘1’ will start

the Analog-to-Digital conversion.

22.2.2

COMPLETION OF A CONVERSION

When the conversion is complete, the ADC module will:

• Clear the GO/DONE bit

• Set the ADIF Interrupt Flag bit

• Update the ADRESH:ADRESL registers with new

conversion result

22.2.3

TERMINATING A CONVERSION

If a conversion must be terminated before completion,

the GO/DONE bit can be cleared in software. The

ADRESH:ADRESL registers will not be updated with

the partially complete Analog-to-Digital conversion

sample. Instead, the ADRESH:ADRESL register pair

will retain the value of the previous conversion.

Additionally, a two TAD delay is required before another

acquisition can be initiated. Following the delay, an

input acquisition is automatically started on the

selected channel.

22.2.4

ADC OPERATION DURING SLEEP

The ADC module can operate during Sleep. This

requires the ADC clock source to be set to the FRC

option. When the FRC clock source is selected, the

ADC waits one additional instruction before starting the

conversion. This allows the SLEEP instruction to be

executed, which can reduce system noise during the

conversion. If the ADC interrupt is enabled, the device

will

wake-up

from

Sleep

when

the

conversion

completes. If the ADC interrupt is disabled, the ADC

module is turned off after the conversion completes,

although the ADON bit remains set.

When the ADC clock source is something other than

FRC, a SLEEP instruction causes the present

conversion to be aborted and the ADC module is

turned off, although the ADON bit remains set.

22.2.5

A/D CONVERSION PROCEDURE

This is an example procedure for using the ADC to

perform an Analog-to-Digital conversion:

Configure Port:

• Disable pin output driver (Refer to the TRIS

• Configure pin as analog (Refer to the ANSEL

Configure the ADC module:

• Select ADC conversion clock

• Select ADC input channel

• Turn on ADC module

Configure ADC interrupt (optional):

• Clear ADC interrupt flag

• Enable ADC interrupt

• Enable peripheral interrupt

• Enable global interrupt(1)

Wait the required acquisition time(2).

Start conversion by setting the GO/DONE bit.

Wait for ADC conversion to complete by one of

the following:

• Polling the GO/DONE bit

• Waiting for the ADC interrupt (interrupts

enabled)

Read ADC Result.

Clear the ADC interrupt flag (required if interrupt

is enabled).

EXAMPLE 22-1:

A/D CONVERSION

Note:

The GO/DONE bit should not be set in the

same instruction that turns on the ADC.

Refer

Section 22.2.5

“A/D

Conversion Procedure”.

Note:

A device Reset forces all registers to their

Reset state. Thus, the ADC module is

turned off and any pending conversion is

terminated.

Note 1: The global interrupt can be disabled if the

user is attempting to wake-up from Sleep

and resume in-line code execution.

2: Refer to Section 22.4 “A/D Acquisition

Requirements”.

;This code block configures the ADC

;for polling, Frc clock and AN0 input.

;

;Conversion start & polling for completion ;

are included.

;

BANKSEL

ADCON1

;

MOVLW

B’01110000’

;Frc clock

MOVWF

ADCON1

;

BANKSEL

TRISGPA

;

BSF

TRISGPA,0

;Set GPA0 to input

BANKSEL

ANSELA

;

BSF

ANSELA,0

;Set GPA0 to analog

BANKSEL

ADCON0

;

MOVLW

B’01000001’

;Select channel AN0

MOVWF

ADCON0

;Turn ADC On

CALL

SampleTime

;Acquisiton delay

BSF

ADCON0,1

;Start conversion

BTFSC

ADCON0,1

;Is conversion done?

GOTO

$-1

;No, test again

BANKSEL

ADRESH

;

MOVF

ADRESH,W

;Read upper 2 bits

MOVWF

RESULTHI

;store in GPR space

BANKSEL

ADRESL

;

MOVF

ADRESL,W

;Read lower 8 bits

MOVWF

RESULTLO

;Store in GPR space

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