7 chapter 7 ADC module

A/D conversion sequence Step1: Configure the A/D module • configure the port pins as analogue inputs, voltage reference, and digital I/O pins, • select A/D converter input channel, • se

CHAPTER 5

ADC ANALOG DIGITAL CONVERTER

Dr Vo Tuong Quan

What is ADC?

•A/D (Analogue-to-Digital) converter is a "mixed signal" circuit which performs digitization of the external analogue signals

•There are 8 bits, 10 bits and 12 bits ADC in PIC family.

Functional

block diagram

of the 12-bit

A/D converter

of the

dsPIC30F4013

device

A/D conversion sequence

Step1: Configure the A/D module

• configure the port pins as analogue inputs, voltage reference, and digital I/O pins,

• select A/D converter input channel,

• select A/D conversion clock,

• select A/D conversion trigger source,

• turn on A/D module;

Step 2: Configure A/D interrupt (if required)

• clear ADIF bit (IFS0,11>),

• select A/D interrupt priority,

• set ADIE bit (IEC0<11>);

Step 3: Start sampling

Step 4: Wait the required acquisition time;

Step 5: Trigger acquisition end, start conversion;

Step 6: Trigger acquisition end, start conversion;

Step 7: Wait for A/D to complete, by either

• waiting for the A/D interrupt, or

• waiting for the DONE bit to get set;

A/D converter configuration

1 - Select voltage reference – This process is performed by

setting the control bit VCFG<2:0> (ADCON2<15:13>)

2 - Select the A/D conversion clock - The A/D conversion

period TAD , generated by a 6-bit counter, is selected by the control bits ADCS<5:0> (ADCON3<5:0>) Period TAD

is defined by the formula:

3 - Selection of analogue inputs - The control bits ADCHS

determine which analogue inputs are selected for each sample

A/D converter configuration

4 - Configuring analogue port pins - The ADPCFG register

specifies the input condition of device pins used as analogue inputs

5 - Enabling the A/D converter module – When the ADON

bit (ADCON1<15>) is set, the module is in active mode and

is fully powered and functional

Manual start of the sampling process – Setting the SAMP

bit (ADCON1<1>)

Automatic start of the sampling process – Setting the

ASAM bit (ADCON1<2>)

A/D Pins on MCU

Example 1: Manual sample start and a manual conversion

start The result of the A/D conversion is sent to the output

of port D.

{device = dsPIC30F6014A

Clock=10MHz}

program Timertest1;

TRISB := $FFFF; //Port B is input

TRISD := 0; //Port D is output (for ADC results)

ADPCFG := $FBFF; //10th channel is sampled and coverted

ADCON1 := $0000; //ADC off, output_format=INTEGER

begin //Manual start of convesion

//Manual start of sampling

ADCHS := $000A; //Connect RB10 on AN10 as CH0 input

ADCSSL := 0; //No scan

ADCON3 := $1003; //ADCS=3 (min TAD for 10MHz is 3*TCY=300ns)

ADCON2 := 0; //Interrupt upon completion of one sample/convert

ADCON1.15 := 1; //ADC on

while TRUE do

begin

ADCON1.1:=1; //Start sampling (SAMP=1)

Delay_ms(100); //Wait for 100ms (sampling )

ADCON1.1:=0; //Clear SAMP bit (trigger conversion)

while ADCON1.0 = 0 do nop; //Wait for DONE bit in ADCON1

LATD := ADCBUF0; //Output result on port D

end;

end.

Example 1: (Cont’d)

Example 2: An automatic sample start and a manual conversion start The result of the conversion is sent to the output of port D.

{device = dsPIC30F6014A

Clock=10MHz}

program Timertest2;

begin

TRISB := $FFFF; //Port B is input

TRISD := 0; //Port D is output (for ADC results)

ADPCFG := $FBFF; //10th channel is sampled and coverted

ADCON1 := $0004; //ADC off, output_format=INTEGER

//Manual start of convesion //Automatic start of sampling after coversion

ADCHS := $000A; //Connect RB10 on AN10 as CH0 input

ADCSSL := 0; //No scan

ADCON3 := $1003; //ADCS=3 (min TAD for 10MHz is 3*TCY=300ns)

ADCON2 := 0; //Interrupt upon completion of one sample/convert

ADCON1.15 := 1; //ADC on

while TRUE do

begin

Delay_ms(100); //Wait for 100ms (sampling )

ADCON1.1:=0; //Clear SAMP bit (trigger conversion)

while ADCON1.1 = 0 do nop; //Wait for DONE bit in ADCON1

LATD:= ADCBUF0; //Output result on port D

end;

end.

Example 2: (Cont’d)

ADC

Using CCS-C compiler in programing ADC function

1 - Setup_ADC ( mode )

ADC_OFF : not use ADC

ADC_CLOCK_INTERNAL: sampling time = MCU clock (2-6 us)

ADC_CLOCK_DIV_2: sampling time = MCU clock/ 2 (0.4 us -when using OSC 20MHz )

ADC_CLOCK_DIV_8 : sampling time = MCU clock/ 8 (1.6 us )

ADC_CLOCK_DIV_32 : sampling time = MCU clock/ 32 (6.4 us)

2 - Setup_ADC_ports ( value )

ALL_ANALOGS ; NO_ANALOG ; AN0_AN1_AN3

3 - Set_ADC_channel ( channel )

4 - Read_ADC ( mode )

ADC_START_AND_READ : default

Example 3:

#include <16F877.h >

#use delay( clock=20000000 )

// ADC 8 bit , ADC : 0-255

#device *= 16 ADC = 8

#FUSES hs,nowdt,noput,nolvp

#byte portB =0x06

#byte portC=0x07

#define RS pin_c0

#define RW pin_c1

#define E pin_c2

Int8 adc, donvi, chuc, tram;

Int8 a =0;

{

output_b(0x38);// config LCD

truyen_lenh();

output_b(0x0E);

truyen_lenh();

Delay_ms (100 );

Setup_ADC ( ADC_internal ) ; Setup_ADC_ports (AN0);

Set_ADC_channel ( 0 ) ;

Delay_us (10 );

While (true ) { adc = read_adc ( ) ;

a = adc;

convert_to_ascii();

hienthi();

} }

Example 3: (Cont’d)

void convert _to_ascii()

{a=a%1000;

tram=a/100 + 0x30;

a=a%100;

chuc= a/10 + 0x30 ;

donvi=a%10 + 0x30;

}

Void hienthi() {

Output_b( 0x80);

Truyen_lenh ; Output_b (‘V’);

Truyen_du_lieu ();

Output_b (donvi);

Truyen_du_lieu ();

Delay_ms (10 );

Output_b ( chuc);

Truyen_du_lieu ();

Delay_ms (10);

Output_b ( tram);

Truyen_du_lieu ();

Delay_ms (10);

}

Example 3: (Cont’d)

void truyen_lenh() //Allow to transmit data to LCD’s register

{output_low(RS);

output_low(RW);

output_high(E);

delay_ms(5);

output_low(E);

delay_ms(5);}

void truyen_du_lieu()//put data to RAM then appear on LCD

{output_high(RS);

output_low(RW);

output_high(E);

delay_ms(5);

output_low(E);

delay_ms(5);

}

Example 4:

void open_adc()

{

setup_adc_ports(RA0_RA1_RA3_ANALOG);

setup_adc( ADC_CLOCK_INTERNAL );

set_adc_channel( 0 );

}

unsigned int32 pro_adc()

{

char i;

adc_value=0;

for(i=1;i<=200;i++)

{

adc_value+=read_adc();

delay_ms(1);

}

adc_value/=200;

return adc_value=adc_weight(adc_value);

}

ADC

DAC – Digital Analog Converter

How can we use DAC module in PIC microcontroller?

What should we need more in order to use this function?

Give examples?