第一節 知識點

1.ADC

（1）10 位模數轉換器（A/D）模塊：28 引腳器件的模數（Analog-to-DigitalA/D）轉換器具有10 路輸入，而40/44 引腳器件的模數轉換器則具有13 路輸入。A/D 模塊能將一個模擬輸入信號轉換成相應的10 位數字信號。

（2）此模塊有五個寄存器：
? A/D 轉換結果高位寄存器（ADRESH）
? A/D 轉換結果低位寄存器（ADRESL）
? A/D 轉換控制寄存器0 （ADCON0）：A/D 模塊的工作方式由ADCON0寄存器控制。
? A/D 轉換控制寄存器1 （ADCON1）：端口引腳的功能由ADCON1 寄存器配置。
? A/D 轉換控制寄存器2 （ADCON2）：由ADCON2 寄存器配置A/D 時鐘源，編程采集時間和對齊方式。

（3）執行A/D 轉換時應該遵循以下步驟：

1. 配置A/D 模塊：
   ? 配置模擬引腳、參考電壓和數字I/O （通過ADCON1 寄存器）
   ? 選擇A/D 輸入通道（通過ADCON0 寄存器）
   ? 選擇A/D 采集時間（通過ADCON2 寄存器）
   ? 選擇A/D 轉換時鐘（通過ADCON2 寄存器）
   ? 使能A/D 模塊（通過ADCON0 寄存器）
2. 需要時，配置A/D 中斷：
   ? 清零ADIF 位
   ? 將ADIE 位置1
   ? 將GIE 位置1
3. 如果需要，等待所需的采集時間。
4. 啟動轉換：
   ? 將GO/DONE 位置1 （ADCON0 寄存器）
5. 等待A/D 轉換完成，通過以下兩種方法之一判斷轉換是否完成：
   ? 查詢GO/DONE 位是否被清零或 等待A/D 中斷
6. 讀取A/D 結果寄存器（ADRESH:ADRESL），需要時將ADIF 位清零。
7. 如需再次進行A/D 轉換，返回步驟1 或步驟2。將每位的A/D 轉換時間定義為TAD，在下一次采集開始前至少需要等待2 個TAD。

（4）A/D 采集要求
為了使A/D 轉換器達到規定精度，必須使充電保持電容（CHOLD）充滿至輸入通道的電平。圖19-3 給出了模擬輸入的電路模型。電源阻抗（RS）和內部采樣開關阻抗（RSS）直接影響電容CHOLD 充電的時間。采樣開關（RSS）阻抗值隨器件電壓（VDD）不同而改變。電源阻抗將影響模擬輸入的偏移電壓（由于引腳泄漏電流的原因）。模擬信號源的最大阻抗推薦值為2.5 kΩ。在選擇（改變）了模擬輸入通道之后，必須對通道進行采樣才能啟動轉換，采樣時間必須大于最小采集時間。

（5） 采樣時間計算：

1.ADC的原理框圖：

2.與ADC相關的寄存器：


我們設置VCFG1=0,采用BSS作為參考電壓VREF-；
設置VCFG0=0，采用VDD作為VREF+的參考電壓。
配置PCFG3:PCFG0 進行采集模擬量的端口配置。

配置ADFM，ADC轉化結構的格式是左對齊還是右對齊，這是因為ADC轉化結果是10位的需要兩個8位寄存器存儲。
ACQT2:ACQT0：A/D 采集時間選擇位；
ADCS2:ADCS0：A/D 轉換時鐘選擇位。

3.比如我們在實際中要采集電壓，典型的電路圖如下：

02第二節 代碼設計

1.我們新建兩個文件：
（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< 
    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< 
    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 采樣
// 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 函數實現成功！
    printf("ADC 采樣實現rtn"); // printf 函數實現成功！
    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;  
}

下載到開發板中看效果吧，代碼的注釋很清楚我就不解釋了。