PIC16F684 datasheet(70/192 Pages) MICROCHIP

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PIC16F684

DS41202F-page 68

9.2

ADC Operation

9.2.1

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.

9.2.2

COMPLETION OF A CONVERSION

When the conversion is complete, the ADC module will:

• Clear the GO/DONE bit

• Set the ADIF flag bit

• Update the ADRESH:ADRESL registers with new

conversion result

9.2.3

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. Addi-

tionally, a 2 TAD delay is required before another acqui-

sition can be initiated. Following this delay, an input

acquisition is automatically started on the selected

channel.

9.2.4

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 conver-

sion to be aborted and the ADC module is turned off,

although the ADON bit remains set.

9.2.5

SPECIAL EVENT TRIGGER

The ECCP Special Event Trigger allows periodic ADC

measurements without software intervention. When

this trigger occurs, the GO/DONE bit is set by hardware

and the Timer1 counter resets to zero.

Using the Special Event Trigger does not ensure

proper ADC timing. It is the user’s responsibility to

ensure that the ADC timing requirements are met.

See

Section 11.0

“Enhanced

Capture/Com-

pare/PWM (With Auto-Shutdown and Dead Band)

Module” for more information.

9.2.6

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 (See TRIS register)

• Configure pin as analog

Configure the ADC module:

• Select ADC conversion clock

• Configure voltage reference

• Select ADC input channel

• Select result format

• 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).

Note:

The GO/DONE bit should not be set in the

same instruction that turns on the ADC.

Refer to Section 9.2.6 “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: See

Section 9.3

“A/D

Acquisition

Requirements”.

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