利用MAX7651實現(xiàn)ADC轉(zhuǎn)換

摘要：本文提供了利用MAX7651評估板實現(xiàn)模/數(shù)轉(zhuǎn)換的源代碼和函數(shù)。它是MAX7651評估板提供的3個應(yīng)用例程之一，能夠進行寫、編譯和下載等簡單的編程功能。

另請參考：

• 為MAX7651評估板配置Keil μVision IDE參數(shù)
• 利用MAX7651評估板的串行下載器將程序裝載到閃存內(nèi)

本文利用8051兼容的微控制器MAX7651實現(xiàn)模/數(shù)轉(zhuǎn)換，并給出了程序代碼。其中包括一些關(guān)鍵的寫操作、編譯和程序下載步驟，支持MAX7651EVKIT進行模數(shù)轉(zhuǎn)換，并可讀取轉(zhuǎn)換結(jié)果。程序使用了MAX7651內(nèi)部的12位集成ADC。

本例源代碼利用Keil DK-51 IDE創(chuàng)建，需要從www.keil.com下載并安裝Keil DK-51演示軟件，以簡化例程使用。Keil程序包含MAX7651基本的庫文件，接下來，應(yīng)該下載μVision2?項目文件和源代碼：AN3083_uVision2_Project_Files.zip。

本例使用MAX7651EVKIT，當然，必要時也可以使用Keil μVision? IDE仿真器演示這些源代碼，無需使用MAX7651EVKIT。軟件安裝請參考MAX7651EVKIT的快速入門使用手冊，其中提供了關(guān)于Keil軟件安裝的詳細信息。

注意：這里提供的例程是Maxim給出的公開源代碼，可以免費復(fù)制，并根據(jù)具體應(yīng)用進行修改。

C程序說明

為了有效使用該例程，需要熟悉C語言編程。程序包括三部分：“ADC Test Function”主程序(main())和兩個調(diào)用子函數(shù)：convert_all_channels()和convert_channel()。主程序首先對MAX7651的寄存器進行初始化，并提供一些標準的庫函數(shù)。然后配置MAX7651，與PC的標準串口進行通信。

主程序main()調(diào)用兩個子函數(shù)，函數(shù)convert_all_channels()順序?qū)?個ADC輸入通道進行轉(zhuǎn)換；函數(shù)convert_channel()能夠使用戶自行選擇轉(zhuǎn)換通道并返回ADC轉(zhuǎn)換結(jié)果。

為了啟動一次轉(zhuǎn)換，只需簡單調(diào)用函數(shù)convert_all_channels()或convert_channel()。函數(shù)通過將所要求的轉(zhuǎn)換通道寫入MAX7651的ADCON寄存器執(zhí)行轉(zhuǎn)換操作，然后通過循環(huán)檢測ADCON寄存器終止轉(zhuǎn)換。轉(zhuǎn)換結(jié)束后，將轉(zhuǎn)換結(jié)果返回到調(diào)用函數(shù)內(nèi)。主程序main()通過調(diào)用stdio.h內(nèi)的printf()函數(shù)，通過串口將結(jié)果顯示在顯示器上。

/*-------------------------------------------------------------------------
ADC Test Function (main.c)
Copyright: Maxim Integrated Products
Target: MAX7651
Date: Feb 26, 2004
Author: Maxim Integrated Products

Description: This program will convert 8 channels using the MAX7651
and send the results to Serial Port 0
--------------------------------------------------------------------------*/
#include 					//include MAX7651 register definitions
#include 					//Standard I/O, Print() function.

#define NUMBER_OF_CHANNELS 8			//Convert 8 channels

void convert_all_channels(int* buffer);			//Function declaration
int convert_channel(int adc_ch);  			//Function declaration

void main(void)					//Begin Main()
{
int Adc_Results[NUMBER_OF_CHANNELS];	//Array to store conversion result
int i;					//for loop counter

	convert_all_channels(Adc_Results);		//Convert all channels, Store results in Adc_Results

	#ifndef MONITOR51			//Setup Serial Port if not using Keil Monitor
SCON  = 0x50;				//9600 Baud, 8N1, Xon, Xoff
	TMOD |= 0x20;
	TH1   = 0xFA;
	TR1   = 1;
	TI    = 1;
	PCON |= 0x80;
	#endif

	for (i=0; i < NUMBER_OF_CHANNELS; i++)	//Display contents to Adc_Results
	{
	printf ("CH %d:%x ",i,Adc_Results[i]);	//print the hex
	}

	printf("
 channel 0 %x", convert_channel(0));		//Convert a single channel and display
	printf("
 channel 1 %x", convert_channel(1));
	printf("
 channel 2 %x", convert_channel(2));
	printf("
 channel 3 %x", convert_channel(3));
   	printf("
 channel 4 %x", convert_channel(4));
	printf("
 channel 5 %x", convert_channel(5));
	printf("
 channel 6 %x", convert_channel(6));
	printf("
 channel 7 %x", convert_channel(7));

	while(1);					//End Program, Start infinite loop since there is no OS
}
 /*-------------------------------------------------------------------------
Function: convert_all_channels
Copyright: Maxim Integrated Products
Target: MAX7651
Date: Feb 26, 2004
Author: Maxim Integrated Products

Usage: The function will return 8 conversion results to an array.

Parameters: p_buffer, pointer to an 8 location array stores the conversion results

Return: Values are returned to the calling function using the function parameters

/*-------------------------------------------------------------------------
Setup ADC in the MAX7651
--------------------------------------------------------------------------*/

sfr ADCON  = 0xC5;				//Define address of  MAX7651 ADCON
sfr ADDAT1 = 0xC3; 				//Define address of  MAX7651 ADDAT1 (8MSBs)
sfr ADDAT0 = 0xC2;				//Define address of MAX7651 ADDAT0 (4LSBs)

void convert_all_channels(int* buffer);
--------------------------------------------------------------------------*/

#define NUMBER_OF_CHANNELS 8

void convert_all_channels(int* p_buffer)            			//pointer Buffer to return
{
	int adc_ch;
	int conv_val;

/*-----------------------------------------------
Convert all ADC channels
-----------------------------------------------*/

	for (adc_ch = 0; adc_ch < NUMBER_OF_CHANNELS; adc_ch++)      //for ADC channels 1 to 7
{

/*-----------------------------------------------
Start a conversion and wait for it to complete.
-----------------------------------------------*/

	ADCON = adc_ch;					//Start conversion and select channel
while ((ADCON & 0x80) == 0);			//wait for conversion to complete
conv_val = (ADDAT0 >> 4) |  (ADDAT1 << 4);		//Format the data in 12 bit format

	  *(p_buffer+adc_ch) = conv_val;		//Write result back to calling function
}					//End For
}						//End function convert_all_channels()

 /*-------------------------------------------------------------------------
Function: convert_channel
Copyright: Maxim Integrated Products
Target: MAX7651
Date: Feb 26, 2004
Author: Maxim Integrated Products

Usage: The function will convert and return the result of a Channel.
Parameters: adc_ch, Select ADC channel to be converted.

Channels 0-7 = single ended channel 0-7.
	Channels 8-11 = differential channel pairs {CH0,1}, {CH2,3}, {CH4,5}, {CH6,7}
	Channel 12 = differential reference measurement {REF+,REF-}

Return: Function returns Integer with the conversion result

Function Declaration: int convert_channel(int adc_ch);
--------------------------------------------------------------------------*/

/*-------------------------------------------------------------------------
Setup ADC in the MAX7651
--------------------------------------------------------------------------*/

sfr ADCON  = 0xC5;				//Define address of  MAX7651 ADCON
sfr ADDAT1 = 0xC3; 				//Define address of  MAX7651 ADDAT1 (8MSBs)
sfr ADDAT0 = 0xC2;				//Define address of MAX7651 ADDAT0 (4LSBs)

int convert_channel(int adc_ch)
{
	int conv_val;

if (ADCON <0 || ADCON >12){		//Check for valid channel
return (-2048);				//Using -FS for the error code
}

	ADCON = adc_ch;				//Select channel and Start conversion
while ((ADCON & 0x80) == 0);		//Wait for the conversion to complete

	conv_val = (ADDAT0 >> 4) |  (ADDAT1 << 4);		//Format the data in 12 bit format

	return (conv_val);					//Return result back to calling function
}							//End function convert_chan