MAX6901 RTC与8051微控制器的接口

要：该应用笔记演示了MAX6901与8051微控制器的连接方式，并提供了基本的接口程序例程。本文采用的微控制器是DS2250，软件用C语言编写。

MAX6901引脚配置
概述该应用笔记演示了MAX6901与8051微控制器的连接方式，并提供了基本的接口程序例程。本文采用的微控制器是DS2250，软件用C语言编写。 工作原理该程序利用微控制器的三个通用端口引脚控制3线总线。微控制器向MAX6901发送一个命令/地址字节，启动数据传输。随后，微控制器向MAX6901发送其它字节或提供SCLK，根据命令字节发送或接收数据。

电路原理图如图1所示，软件如图2所示。


图1. 子卡原理图"(PDF下载)

图2. 代码列表

/***************************************************************************/
/* DEMO6901.c                                                              */
/***************************************************************************/
/* #pragma code symbols debug */
#include 		/* Register declaraTIons for DS5000 */
/***************************** Defines ********************************/
sbit CE      = P0^0;
sbit SCLK    = P0^1;
sbit IO     = P0^2;
/*********************** FuncTIon Prototypes **************************/
void	writebyte();
void	iniTIalize();
void	disp_clk_regs();
void	burstramread();
void	burstramwrt();
/************************* Global Variables ***************************/
uchar	cy, yr, mn, dt, dy, hr, min, sec, msec;

void reset_3w()	/* ---- reset the 3-wire interface ---- */
{
	SCLK = 0;
	CE = 0;
	IO = 0;	/* program IO pin to 0V */
}
void wbyte_3w(uchar W_Byte)	/* --- write one byte to the DUT --- */
{
uchar i;

	CE = 1;
	for(i = 0; i < 8; ++i)
	{
		if(W_Byte & 0x01)
			IO = 1;	/* set port pin high to read data */
		else
			IO = 0;
		SCLK = 0;
		SCLK = 1;
		W_Byte >>= 1;
      }
}
uchar rbyte_3w()	/* --- read one byte from the DUT --- */
{
uchar i;
uchar R_Byte = 0;

	CE = 1;
	IO = 1;
	for(i=0; i<8; ++i)
	{
		SCLK = 1;
		SCLK = 0;
		if(IO)
		{
			R_Byte >>= 1;
			R_Byte += 0x80;
		}
		else
			R_Byte >>= 1;
	}
	return R_Byte;
}
void writebyte()	/* ----- write one byte, prompt for address and data ------ */
{
uchar add;
uchar dat;
	/* Get Address & Data */
	printf("
Enter the Write Address (h)
ADDRESS (80,82,84...):");
	scanf("%bx", &add);
	printf("DATA (0-ff):");
	scanf("%bx", &dat);

	reset_3w();
	wbyte_3w(add);
	wbyte_3w(dat);
	reset_3w();
}
void iniTIalize()	/* ----- init clock data using user entries ----- */
/* Note: NO error checking is done on the user entries! */
{
	reset_3w();
	wbyte_3w(0x0f);		/* control register write address */
	wbyte_3w(0x00);		/* clear write protect */
	reset_3w();

	printf("
Enter the year (0-99): ");
	scanf("%bx", &yr);
	printf("Enter the month (1-12): ");
	scanf("%bx", &mn);
	printf("Enter the date (1-31): ");
	scanf("%bx", &dt);
	printf("Enter the day (1-7): ");
	scanf("%bx", &dy);
	printf("Enter the hour (1-23): ");
	scanf("%bx", &hr);
	hr = hr & 0x3f;	/* force clock to 24 hour mode */
	printf("Enter the minute (0-59): ");
	scanf("%bx", &min);
	printf("Enter the second (0-59): ");
	scanf("%bx", &sec);

	reset_3w();
	wbyte_3w(0xbe);	/* clock burst write */
	wbyte_3w(sec);
	wbyte_3w(min);
	wbyte_3w(hr);
	wbyte_3w(dt);
	wbyte_3w(mn);
	wbyte_3w(dy);
	wbyte_3w(yr);
	wbyte_3w(0);		/* control */
	reset_3w();
	wbyte_3w(0x92);
	wbyte_3w(0x20);	/* century data */
	reset_3w();
}
void disp_clk_regs()		/* --- loop reading clock, display when secs change --- */
{
uchar mil, pm, prv_sec = 99;

while(!RI)	/* Read & Display Clock Registers */
{
	reset_3w();
	wbyte_3w(0xbf);	/* clock burst read */
	sec = rbyte_3w();
	min = rbyte_3w();
	hr = rbyte_3w();
	dt = rbyte_3w();
	mn = rbyte_3w();
	dy = rbyte_3w();
	yr = rbyte_3w();
	cy = rbyte_3w();	/* dummy read of control register */
	reset_3w();
	wbyte_3w(0x93);	/* century byte read address */
	cy  = rbyte_3w();
	reset_3w();

	if(hr & 0x80)
		mil = 0;
	else
		mil = 1;

	if(sec != prv_sec)	/* display every time seconds change */
	{
		if(mil)
		{
			printf("
%02bX%02bX/%02bX/%02bX %01bX", cy, yr, mn, dt, dy);
			printf(" %02bX:%02bX:%02bX", hr, min, sec);
		}
		else
		{
			if(hr & 0x20)
				pm = 'P';
			else
				pm = 'A';
			hr &= 0x1f;	/* strip mode and am/pm bits */
			printf("
%02bx%02bx/%02bx/%02bx %02bx", cy, yr, (mn & 0x1f), dt, dy);
			printf(" %02bx:%02bx:%02bx %cM", hr, min, sec, pm);
		}
	}
	prv_sec = sec;
}
   RI = 0;  /* Swallow keypress to exit loop */
}
void burstramread()		/* ------ read RAM using burst mode ----- */
{
uchar k;

	printf("
MAX6901 RAM contents:
");

	reset_3w();
	wbyte_3w(0xff);	/* ram burst read */
	for (k = 0; k < 31; k++)
	{
		if(!(k % 8) )	printf("
");
		printf("%02.bX ", rbyte_3w() );
	}
	reset_3w();
}
void burstramwrt(uchar Data)	/* ------ write RAM using burst mode ------- */
{
uchar j, k;

	reset_3w();
	wbyte_3w(0xfe);	/* ram burst write */
	for (k=0; k < 31; ++k)
	{
		wbyte_3w(Data);
	}
	reset_3w();
}
main (void)		/* ----------------------------------------------------- */
{
uchar i, M, M1;

	while (1)
	{
		printf("
MAX6901 build %s
", __DATE__);
		printf("CI Clock Init
");
		printf("CR Clock Read CW Clock Write
");
		printf("RR Read RAM   RW RAM Write
");
		printf("Enter Menu Selection: ");

		M = _getkey();

		switch(M)
		{
			case 'C':
			case 'c':
			printf("\rEnter Clock Routine to run:C");
			M1 = _getkey();

			switch(M1)
			{
				case 'I':
				case 'i':	initialize();
						break;

				case 'R':
				case 'r':	disp_clk_regs();
					      break;

				case 'W':
				case 'w':	writebyte();
						break;
			}
			break;

			case 'R':
			case 'r':
			printf("\rEnter Ram Routine to run:R");
			M1 = _getkey();

			switch(M1)
			{
				case 'R':
				case 'r':	burstramread();
						break;
				case 'W':
				case 'w':	printf("
Enter the data to write: ");
						scanf("%bx", &i);
						burstramwrt(i);	break;
			}
			break;
		}
	}
}