Simple digital voltmeter + ADC0809 + interrupt mode to achieve one-way data conversion

1 Experimental Phenomenon

2 Experimental Principle

The working process of ADC0809: First input the 3-bit address and make ALE=1, and input the address into the address latch. This address is decoded to select one of the 8 analog inputs to the comparator. The rising edge of START will gradually approach the register reset. The falling edge starts the ADC conversion, and then the EOC output signal becomes low, indicating that the conversion is in progress. Until the ADC conversion is completed, EOC becomes a high level, indicating that the ADC conversion is over, and the result data has been stored in the latch. This signal can be used as an interrupt request. When the OE input is high, the output tri-state gate is opened, and the digital value of the conversion result is output to the data bus. Common software control methods for AD conversion are:

(1) Program query method

First, the microprocessor sends a start signal to the A/D converter, then reads the conversion end signal, and queries whether the conversion is completed. If it is completed, read the data, otherwise continue to query until the conversion is completed. This method is simple and reliable, but the query takes up CPU time and is less efficient.

(2) Delayed waiting method

After the microprocessor sends a start signal to the A/D converter, it delays according to the conversion time of the A/D converter. Generally, the delay time is slightly longer than the conversion time of the A/D converter. When the delay ends, the data is read in. This method is simple and does not occupy the query port, but it occupies CPU time and has low efficiency. It is suitable for situations where the microprocessor has few processing tasks.

(3) Interrupt mode

After the microprocessor starts the A/D conversion, it can handle other things. After the A/D conversion is completed, it will actively send an interrupt request signal to the CPU. The CPU responds to the interrupt and then reads the conversion result. The microprocessor can work in parallel with the A/D converter, which improves efficiency.

3 System Design

4 Hardware Design

(1) ADC0809 cannot be simulated normally in Proteus software, but ADC0808 can be simulated normally, so ADC0808 is used instead;

(2) The CLOCK of ADC0809 is typically 500KHz, which is obtained by using the ALE (2MHz) of the microcontroller through a four-frequency division circuit;

(3) Output of ADC0809, mainly the order of high and low bits;

(4) EOC, connect the microcontroller external interrupt EX0, P3.2, the trigger mode is falling edge trigger, and add an inverter between EOC and P3.2.

(5) The ALE pin does not have a 6-frequency pulse output. Setting method: Reset the microcontroller. In the Advanced Properties option, select Simulate program Fetches and select YES.

5 Software Design

5.1 Main Program

#include "DisplaySmg.h"

#include "ADC0809.h"

#include "Timer0.h"

int adc_result_show = 0;

unsigned char adc_flag = 1; // Flag signal to start ADC conversion

void disp_num() //Put the data to be displayed into the buffer

{

LedBuf[0]= 23; //Thousands, not displayed

LedBuf[1]= adc_result_show/100; //hundreds place

LedBuf[2]= adc_result_show/10%10; //ten digit

LedBuf[3]= adc_result_show%10; //unit digit

}

void main()

{

Timer0_Init(); //Timer counter T0 initialization

EX0_Init(); //External interrupt initialization

EA=1; //Interrupt main switch

DotDig1=1; //light up the decimal point of the second digital tube

while(1)

{

if(adc_flag==1) //Start ADC conversion every 500ms

{

adc_flag = 0;

Start_ADC0809(); //Filtering, cannot sample only once, multiple sampling digital filtering should be performed

adc_result_show = adc_result*1.0*100*5/255; //Data conversion processing (linear scale conversion)

disp_num(); //Display data

}

}

}

void Timer0_ISR(void) interrupt 1

{

static unsigned int timer0cnt=0;

TR0=0; //Turn off the timer

timer0cnt++;

if(timer0cnt>=500)

{

timer0cnt = 0;

adc_flag = 1; //500ms flag signal

}

DisplaySmg(); //Refresh the digital tube display function every 1ms

TL0 = 0x66; //Set the initial timing value, timing 1ms

TH0 = 0xFC; //Set the initial timing value, timing 1ms

TR0=1; //Turn on the timer

}

5.2 ACD0809 analog-to-digital conversion module

#ifndef __ADC0809_H__

#define __ADC0809_H__

#include

#define ADC_DATA P1

sbit ADDR_A = P3^7;

sbit ADDR_B = P3^6;

sbit ADDR_C = P3^5;

sbit START = P3^4;

sbit EOC = P3^2;

sbit OE = P3^3;

extern unsigned char adc_result;

void Start_ADC0809();

void EX0_Init();

#endif

#include "ADC0809.h"

unsigned char adc_result;

void Start_ADC0809()

{

OE = 0; //Data output enable signal, high level is valid

START = 0; //ADC conversion start signal, high level is valid, connected with ALE (address latch enable signal) in the circuit

ADDR_A = 1; //3-bit address input line

ADDR_B = 1; //Used to select one of the 8 analog inputs

ADDR_C = 0;

START = 1; //Rising edge, clear the register inside the ADC

START = 0; //Generate a certain pulse, Typ = 100ns, the falling edge starts AD conversion

}

void EX0_Init() //External interrupt initialization

{

IT0 = 1; //External interrupt 0, set to falling edge trigger

EX0 = 1; //External interrupt 0 switch

}

void EX0_ISR() interrupt 0

{

OE = 1;

adc_result = ADC_DATA;

OE = 0;

}

5.3 Digital tube dynamic display module

#ifndef __DisplaySmg_H__

#define __DisplaySmg_H__

#include

#define GPIO_SEG P0 //Segment select port

#define GPIO_SEL P2 //bit select port

extern unsigned char LedBuf[]; //external variable declaration

extern unsigned char DotDig0,DotDig1,DotDig2,DotDig3;

void DisplaySmg(void);

#endif

#include "DisplaySmg.h"

unsigned char code LedData[]={ //segment code table, character, serial number of common cathode digital tube

0x3F, //"0", 0

0x06, //"1", 1

0x5B, //"2", 2

0x4F, //"3", 3

0x66, //"4", 4

0x6D, //"5", 5

0x7D, //"6", 6

0x07, //"7", 7

0x7F, //"8", 8

0x6F, //"9", 9

0x77, //"A", 10

0x7C, //"B", 11

0x39, //"C", 12

0x5E, //"D", 13

0x79, //"E", 14

0x71, //"F", 15

0x76, //"H", 16

0x38, //"L", 17

0x37, //"n", 18

0x3E, //"u", 19

0x73, //"P", 20

0x5C, //"o", 21

0x40, //"-", 22

0x00, //turn off 23

};

unsigned char DotDig0=0,DotDig1=0,DotDig2=0,DotDig3=0; //decimal point control bit

unsigned char code LedAddr[]={0xfe,0xfd,0xfb,0xf7}; //digital tube position selection

unsigned char LedBuf[]={22,22,22,22}; //Display buffer area

void DisplaySmg() //Four-digit digital tube, consider the decimal point

{

unsigned char i; // equivalent to "static unsigned char i = 0;"

unsigned char temp;

switch(i)

{

case 0:

{

GPIO_SEG = 0x00; //Eliminate shadow

if(DotDig0==1) //decimal point

{

temp = LedData[LedBuf[0]] | 0x80; //Light up the decimal point

}

else

{

temp = LedData[LedBuf[0]];

}

GPIO_SEG = temp; //segment code

GPIO_SEL = LedAddr[0]; //bit selection

i++;

break;

}

case 1:

GPIO_SEG = 0x00;

if(DotDig1==1) //decimal point

{

temp = LedData[LedBuf[1]] | 0x80;

}

else

{

temp = LedData[LedBuf[1]];

}

GPIO_SEG = temp;

GPIO_SEL = LedAddr[1];

i++;

break;

case 2:

GPIO_SEG = 0x00;

if(DotDig2==1) //decimal point

{

temp = LedData[LedBuf[2]] | 0x80;

}

else

{

temp = LedData[LedBuf[2]];

}

GPIO_SEG = temp;

GPIO_SEL = LedAddr[2];

i++;

break;

case 3:

GPIO_SEG = 0x00;

if(DotDig3==1) //decimal point

{

temp = LedData[LedBuf[3]] | 0x80;

}

else

{

temp = LedData[LedBuf[3]];

}

GPIO_SEG = temp;

GPIO_SEL = LedAddr[3];

i=0;

break;

default:break;

}

}

5.4 Timer T0 module

#ifndef __Timer0_H__

#define __Timer0_H__

#include

void Timer0_Init(void);

#endif

#include "Timer0.h"

void Timer0_Init(void) //1 millisecond @ 11.0592MHz

{

TMOD &= 0xF0; //Set timer mode

TMOD |= 0x01; //Set timer mode

TL0 = 0x66; //Set the initial value of the timing

TH0 = 0xFC; //Set the initial value of the timing

TF0 = 0; // Clear TF0 flag

TR0 = 1; //Timer 0 starts timing

ET0 = 1; //Timer 0 interrupt switch

//EA = 1; //Interrupt main switch

}

//The interrupt service function must be a function without a return value

//The interrupt service function must be a function without parameters

//Interrupt service function function name followed by the keyword interrupt

//interrupt n 0~4 5 interrupt sources, 8*n+0003H

// 0003H INT0, 00BH T0, 0013H INT1, 001BH T1, 0023H ES

//The interrupt service function cannot be called by the main program or other programs

//n is followed by using m (0~3) working register group

//void Timer0_ISR(void) interrupt 1

//{

// TL0 = 0x66; //Set the initial timing value

// TH0 = 0xFC; //Set the initial value of the timing

//}

6 References

(1) Single chip microcomputer application - ADC0809 interrupt mode to realize A/D conversion of one analog signal (digital tube display)_bilibili_bilibili;