摘要
本文提供了利用MAX7651评估板实现模/数转换的源代码和函数。它是MAX7651评估板提供的3个应用例程之一，能够进行写、编译和下载等简单的编程功能。
另请参考：
本文利用8051兼容的微控制器MAX7651实现模/数转换，并给出了程序代码。其中包括一些关键的写操作、编译和程序下载步骤，支持MAX7651EVKIT进行模数转换，并可读取转换结果。程序使用了MAX7651内部的12位集成ADC。本例源代码利用Keil DK-51 IDE创建，需要从www.keil.com下载并安装Keil DK-51演示软件，以简化例程使用。Keil程序包含MAX7651基本的库文件，接下来，应该下载µVision2®项目文件和源代码：AN3083_uVision2_Project_Files.zip。
本例使用MAX7651EVKIT，当然，必要时也可以使用Keil µVision® IDE仿真器演示这些源代码，无需使用MAX7651EVKIT。软件安装请参考MAX7651EVKIT的快速入门使用手册，其中提供了关于Keil软件安装的详细信息。
注意：这里提供的例程是Maxim给出的公开源代码，可以免费复制，并根据具体应用进行修改。
C程序说明
为了有效使用该例程，需要熟悉C语言编程。程序包括三部分：“ADC Test Function”主程序(main())和两个调用子函数：convert_all_channels()和convert_channel()。主程序首先对MAX7651的寄存器进行初始化，并提供一些标准的库函数。然后配置MAX7651，与PC的标准串口进行通信。
主程序main()调用两个子函数，函数convert_all_channels()顺序对8个ADC输入通道进行转换；函数convert_channel()能够使用户自行选择转换通道并返回ADC转换结果。
为了启动一次转换，只需简单调用函数convert_all_channels()或convert_channel()。函数通过将所要求的转换通道写入MAX7651的ADCON寄存器执行转换操作，然后通过循环检测ADCON寄存器终止转换。转换结束后，将转换结果返回到调用函数内。主程序main()通过调用stdio.h内的printf()函数，通过串口将结果显示在显示器上。
/*-------------------------------------------------------------------------
ADC Test Function (main.c)
Copyright: Maxim Integrated
Target: MAX7651
Date: Feb 26, 2004
Author: Maxim Integrated
Description: This program will convert 8 channels using the MAX7651
and send the results to Serial Port 0
--------------------------------------------------------------------------*/
#include <reg51.h> //include MAX7651 register definitions
#include <stdio.h> //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
Target: MAX7651
Date: Feb 26, 2004
Author: Maxim Integrated
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
Target: MAX7651
Date: Feb 26, 2004
Author: Maxim Integrated
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
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