PIC16C781 datasheet(76/186 Pages) MICROCHIP

76 / 186 page

PIC16C781/782

DS41171A-page 74

Preliminary

 2001 Microchip Technology Inc.

FIGURE 9-2:

ANALOG INPUT MODEL

9.4

ADC Configuration and

Conversion

Example 9-2 demonstrates an ADC conversion. The

RA0/AN0 pin is configured as the analog input. The ref-

erence voltage selected is the device AVDD. The ADC

interrupt is enabled, and the ADC conversion clock is

ADRC.

Clearing the GO/DONE bit during a conversion aborts

the current conversion. The ADRES register is NOT

updated with the partially completed ADC conversion

sample. That is, the ADRES register continues to con-

tain the value of the last completed conversion (or the

last value written to the ADRES register). After the ADC

conversion is aborted, a 2TAD wait period is required

before the next acquisition is started. After this 2TAD

wait period, an acquisition is automatically started on

the selected channel.

EXAMPLE 9-2:

ADC CONVERSION

;********************************************

This code block will configure the ADC

for polling, AVDD as reference, RC clock

and RA0 input.

Conversion start & wait for complete

polling code included.

BANKSEL

ADCON1

;

Select Bank 1

CLRF

ADCON1

; AVDD as VREF

BSF

TRISA,0

; Set RA0 as input

BSF

ANSEL,0

; Set RA0 as analog

BANKSEL

ADCON0

; Select Bank0

MOVLW

B’11000001’

MOVWF

ADCON0

; RC, Ch 0, ADC on

;********************************************

Start & Wait for ADC complete, assumes

minimum acquisition delay from

configuration.

ADC_CNVRT

BANKSEL

ADCON0

; Select Bank 0

BSF

ADCON0,GO

; Start convert

ADC_CN_LOOP

BTFSC

ADCON0,GO

; Test for end

GOTO

ADC_CN_LOOP ; If not, wait

MOVF

ADRES,W

; Get result

CPIN

ANx

5 pF

VDD

VT = 0.6V

ILEAKAGE

RIC

≤ 1k

Sampling

Switch

RSS

CHOLD

= DAC capacitance

VSS

Sampling Switch

567 8 9 10 11

( k

Ω )

VDD

= 51.2 pF

± 500 nA

Legend: CPIN

ILEAKAGE

RIC

CHOLD

= input capacitance

= threshold voltage

= leakage current at the pin due to

= interconnect resistance

= sampling switch

= sample/hold capacitance (from DAC)

various junctions

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