PIC16F684-ESLASHST datasheet(65/164 Pages) MICROCHIP

65 / 164 page

 2004 Microchip Technology Inc.

Preliminary

DS41202C-page 63

PIC16F684

9.0

ANALOG-TO-DIGITAL

CONVERTER (A/D) MODULE

The Analog-to-Digital converter (A/D) allows conver-

sion of an analog input signal to a 10-bit binary repre-

sentation of that signal. The PIC16F684 has eight

analog inputs, multiplexed into one sample and hold

circuit. The output of the sample and hold is connected

to the input of the converter. The converter generates a

binary result via successive approximation and stores

the result in a 10-bit register. The voltage reference

used in the conversion is software selectable to either

VDD or a voltage applied by the VREF pin. Figure 9-1

shows the block diagram of the A/D on the PIC16F684.

FIGURE 9-1:

A/D BLOCK DIAGRAM

9.1

A/D Configuration and Operation

There are three registers available to control the

functionality of the A/D module:

ANSEL (Register 9-1)

ADCON0 (Register 9-2)

ADCON1 (Register 9-3)

9.1.1

ANALOG PORT PINS

The ANS<7:0> bits (ANSEL<7:0>) and the TRIS bits

control the operation of the A/D port pins. Set the

corresponding TRIS bits to set the pin output driver to

its high-impedance state. Likewise, set the correspond-

ing ANSEL bit to disable the digital input buffer.

9.1.2

CHANNEL SELECTION

There are eight analog channels on the PIC16F684,

AN0

through

AN7.

The

CHS<2:0>

bits

(ADCON0<4:2>) control which channel is connected to

the sample and hold circuit.

9.1.3

VOLTAGE REFERENCE

There are two options for the voltage reference to the

A/D converter: either VDD is used, or an analog voltage

applied to VREF is used. The VCFG bit (ADCON0<6>)

controls the voltage reference selection. If VCFG is set,

then the voltage on the VREF pin is the reference;

otherwise, VDD is the reference.

RA0/AN0

A/D

RA1/AN1/VREF

RA2/AN2

RC0/AN4

VDD

VREF

ADON

GO/DONE

VCFG = 1

VCFG = 0

CHS<2:0>

ADRESH

ADRESL

ADFM

VSS

RC1/AN5

RC2/AN6

RC3/AN7

RA4/AN3

Note:

Analog voltages on any pin that is defined

as a digital input may cause the input

buffer to conduct excess current.

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