Microchip PIC系列8位单片机入门教程(6)ADC

电子发烧友网 2023年07月15日 14:48

      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

/* MicrochipTechnology 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 TRISAvoidADC_Channel_config(void); doubleADC_Converter_Ddecimal(unsignedint ADC_data); doubleADC_Process_show(unsignedchar Channel_selected ); doubleADC_Process_Select_work(unsignedchar Channel_selected); #endif/* XC_HEADER_TEMPLATE_H */

      （2）adc_sample.c

#include#include"adc_sample.h"staticunsignedint ADC_Data[8]=0; voidADC_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. */doubleADC_Converter_Ddecimal(unsignedint ADC_data){ double temp; temp=(double) ADC_data*5.0; return temp/1023.0; } /* * This is first way to get ADC sample Result. */doubleADC_Process_show(unsignedchar Channel_selected){ double ADC_temp0=0; switch (Channel_selected){ case0: ADC_Channel_select=Channel_0_ON; break; case1: ADC_Channel_select=Channel_1_ON; break; case2: ADC_Channel_select=Channel_2_ON; break; case3: ADC_Channel_select=Channel_3_ON; break; case4: ADC_Channel_select=Channel_4_ON; break; case5: ADC_Channel_select=Channel_5_ON; break; case6: ADC_Channel_select=Channel_6_ON; break; case7: 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. */doubleADC_Process_Select_work(unsignedchar 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"intmain(void){ unsignedchar 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); } return0; }

      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。

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