Microchip PIC系列8位单片机入门教程(6)ADC

第一节 知识点

1.ADC

（1）10 位模数转换器（A/D）模块：28 引脚器件的模数（Analog-to-DigitalA/D）转换器具有10 路输入，而40/44 引脚器件的模数转换器则具有13 路输入。A/D 模块能将一个模拟输入信号转换成相应的10 位数字信号。

（2）此模块有五个寄存器：
• A/D 转换结果高位寄存器（ADRESH）
• A/D 转换结果低位寄存器（ADRESL）
• A/D 转换控制寄存器0 （ADCON0）：A/D 模块的工作方式由ADCON0寄存器控制。
• A/D 转换控制寄存器1 （ADCON1）：端口引脚的功能由ADCON1 寄存器配置。
• A/D 转换控制寄存器2 （ADCON2）：由ADCON2 寄存器配置A/D 时钟源，编程采集时间和对齐方式。

（3）执行A/D 转换时应该遵循以下步骤：

1. 配置A/D 模块：
   • 配置模拟引脚、参考电压和数字I/O （通过ADCON1 寄存器）
   • 选择A/D 输入通道（通过ADCON0 寄存器）
   • 选择A/D 采集时间（通过ADCON2 寄存器）
   • 选择A/D 转换时钟（通过ADCON2 寄存器）
   • 使能A/D 模块（通过ADCON0 寄存器）
2. 需要时，配置A/D 中断：
   • 清零ADIF 位
   • 将ADIE 位置1
   • 将GIE 位置1
3. 如果需要，等待所需的采集时间。
4. 启动转换：
   • 将GO/DONE 位置1 （ADCON0 寄存器）
5. 等待A/D 转换完成，通过以下两种方法之一判断转换是否完成：
   • 查询GO/DONE 位是否被清零或 等待A/D 中断
6. 读取A/D 结果寄存器（ADRESH:ADRESL），需要时将ADIF 位清零。
7. 如需再次进行A/D 转换，返回步骤1 或步骤2。将每位的A/D 转换时间定义为TAD，在下一次采集开始前至少需要等待2 个TAD。

（4）A/D 采集要求
为了使A/D 转换器达到规定精度，必须使充电保持电容（CHOLD）充满至输入通道的电平。图19-3 给出了模拟输入的电路模型。电源阻抗（RS）和内部采样开关阻抗（RSS）直接影响电容CHOLD 充电的时间。采样开关（RSS）阻抗值随器件电压（VDD）不同而改变。电源阻抗将影响模拟输入的偏移电压（由于引脚泄漏电流的原因）。模拟信号源的最大阻抗推荐值为2.5 kΩ。在选择（改变）了模拟输入通道之后，必须对通道进行采样才能启动转换，采样时间必须大于最小采集时间。

（5） 采样时间计算：

1.ADC的原理框图：

2.与ADC相关的寄存器：


我们设置VCFG1=0,采用BSS作为参考电压VREF-；
设置VCFG0=0，采用VDD作为VREF+的参考电压。
配置PCFG3:PCFG0 进行采集模拟量的端口配置。

配置ADFM，ADC转化结构的格式是左对齐还是右对齐，这是因为ADC转化结果是10位的需要两个8位寄存器存储。
ACQT2:ACQT0：A/D 采集时间选择位；
ADCS2:ADCS0：A/D 转换时钟选择位。

3.比如我们在实际中要采集电压，典型的电路图如下：

02第二节 代码设计

1.我们新建两个文件：
（1） adc_sample.h

/* Microchip Technology Inc. and its subsidiaries.  You may use this software
* and any derivatives exclusively with Microchip products.
* File:   adc_sample.h
* Author: Greg
* Comments:
* Revision history:  2018-06-21
*/


// This is a guard condition so that contents of this file are not included
// more than once. 
#ifndef _ADC_SAMPLE_H_
#define           _ADC_SAMPLE_H_


#include // include processor files - each processor file is guarded. 


#define Channel_0_ON 0b0000
#define Channel_1_ON 0b0001
#define Channel_2_ON 0b0010
#define Channel_3_ON 0b0011
#define Channel_4_ON 0b0100
#define Channel_5_ON 0b0101
#define Channel_6_ON 0b0110
#define Channel_7_ON 0b0111
#define ADC_Channel_select ADCON0bits.CHS
#define ADC_ENABLE ADCON0bits.ADON=1
#define ADC_DISABLE ADCON0bits.ADON=0
#define ADC_STATUS ADCON0bits.GODONE
#define ADC_START ADCON0bits.GO=1
#define ADC_PORT_DIR TRISA


void ADC_Channel_config(void);
double ADC_Converter_Ddecimal(unsigned int ADC_data);
double ADC_Process_show(unsigned char Channel_selected );
double ADC_Process_Select_work(unsigned char Channel_selected);
#endif           /* XC_HEADER_TEMPLATE_H */

（2）adc_sample.c

#include
#include "adc_sample.h"
static unsigned int  ADC_Data[8]=0;
void ADC_Channel_config(void)
{
    ADC_PORT_DIR=0xFF;
    ADCON1bits.PCFG=0b0111; //select An0-An7 Channel to A_D converter
    ADCON1bits.VCFG=0b00;   //voltage reference for Vss,Vdd.
    ADCON2bits.ADFM=1;  // reslut right justed
    ADCON2bits.ACQT=0b001;
    ADCON2bits.ADCS=0b000;
}
/*
this fucntion is to converter result of ADC to decimal result.
*/
double ADC_Converter_Ddecimal(unsigned int ADC_data)
{   double temp;
    temp=(double) ADC_data*5.0;
     return temp/1023.0;
}


/*
* This is first way to get ADC sample Result.
*/
double ADC_Process_show(unsigned char Channel_selected)
{ 
    double ADC_temp0=0;
    switch (Channel_selected){
            case 0:
                ADC_Channel_select=Channel_0_ON;
                break;
            case 1:
                ADC_Channel_select=Channel_1_ON;   
                break;
            case 2:
                ADC_Channel_select=Channel_2_ON;   
                break;
            case 3:
                ADC_Channel_select=Channel_3_ON;   
                break;
            case 4:
                ADC_Channel_select=Channel_4_ON;   
                break;
            case 5:
                ADC_Channel_select=Channel_5_ON;   
                break;
            case 6:
                ADC_Channel_select=Channel_6_ON;   
                break;
            case 7:
                ADC_Channel_select=Channel_7_ON;   
                break;}
    ADC_ENABLE;
    ADC_START;
    while(ADC_STATUS);
//    ADC_Data[0]=0x00FF&ADRESL;
//    ADC_Data[0]|=ADRESH< < 8;< span="" >
    ADC_Data[0]=ADRES;
    ADC_temp0=ADC_Converter_Ddecimal(ADC_Data[Channel_selected]);
    return ADC_temp0;
}




/*
* This is second way to get ADC sample Result.
*/


double ADC_Process_Select_work(unsigned char Channel_selected)
{   double ADC_temp0=0;
    ADC_Channel_select=Channel_selected;
    ADC_ENABLE;
    ADC_START;
    while(ADC_STATUS);
//    ADC_Data[0]=0x00FF&ADRESL;
//    ADC_Data[0]|=ADRESH< < 8;< span="" >
    ADC_Data[0]=ADRES;
    ADC_temp0=ADC_Converter_Ddecimal(ADC_Data[0]);
    return ADC_temp0;
}

（3）main.C

// PIC18F4520 Configuration Bit Settings


// 'C' source line config statements
// Author:Greg
// Title:ADC 采样
// CONFIG1H
#pragma config OSC = HS         // Oscillator Selection bits (HS oscillator)
#pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor disabled)
#pragma config IESO = OFF       // Internal/External Oscillator Switchover bit (Oscillator Switchover mode disabled)


// CONFIG2L
#pragma config PWRT = OFF       // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = SBORDIS  // Brown-out Reset Enable bits (Brown-out Reset enabled in hardware only (SBOREN is disabled))
#pragma config BORV = 3         // Brown Out Reset Voltage bits (Minimum setting)


// CONFIG2H
#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT disabled (control is placed on the SWDTEN bit))
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)


// CONFIG3H
#pragma config CCP2MX = PORTC   // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = ON      // PORTB A/D Enable bit (PORTB< 4:0 >pins are configured as analog input channels on Reset)
#pragma config LPT1OSC = OFF    // Low-Power Timer1 Oscillator Enable bit (Timer1 configured for higher power operation)
#pragma config MCLRE = OFF      // MCLR Pin Enable bit (RE3 input pin enabled; MCLR disabled)


// CONFIG4L
#pragma config STVREN = OFF     // Stack Full/Underflow Reset Enable bit (Stack full/underflow will not cause Reset)
#pragma config LVP = OFF        // Single-Supply ICSP Enable bit (Single-Supply ICSP disabled)
#pragma config XINST = OFF      // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode disabled (Legacy mode))


// CONFIG5L
#pragma config CP0 = OFF        // Code Protection bit (Block 0 (000800-001FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection bit (Block 1 (002000-003FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection bit (Block 2 (004000-005FFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection bit (Block 3 (006000-007FFFh) not code-protected)


// CONFIG5H
#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot block (000000-0007FFh) not code-protected)
#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)


// CONFIG6L
#pragma config WRT0 = OFF       // Write Protection bit (Block 0 (000800-001FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (002000-003FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection bit (Block 2 (004000-005FFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection bit (Block 3 (006000-007FFFh) not write-protected)


// CONFIG6H
#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)
#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot block (000000-0007FFh) not write-protected)
#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)


// CONFIG7L
#pragma config EBTR0 = OFF      // Table Read Protection bit (Block 0 (000800-001FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (002000-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection bit (Block 2 (004000-005FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection bit (Block 3 (006000-007FFFh) not protected from table reads executed in other blocks)


// CONFIG7H
#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot block (000000-0007FFh) not protected from table reads executed in other blocks)


// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.


#include
#include "adc_sample.h"
#include
#include "usart_dr.h"
//#include"plib/adc.h"
//#include "delays.h"
int main(void)
{  
   unsigned char Channel_select=0;
    double ADC_temp0;
    ADC_Channel_config(); 
    usart_port_dir_init();
    usart_Config_init();
    printf("test for printf functionrtn"); // printf 函数实现成功！
    printf("ADC 采样实现rtn"); // printf 函数实现成功！
    while(1)
    {
       ADC_temp0=ADC_Process_show(Channel_select);
       printf("ADC var:%frtn",ADC_temp0);
       ADC_temp0=ADC_Process_Select_work(Channel_0_ON);
        printf("ADC var:%frtn",ADC_temp0);
    }
     return 0;  
}

下载到开发板中看效果吧，代码的注释很清楚我就不解释了。