MAX6902 RTC于8051微控制器的接口

摘要：该应用笔记提供了MAX6902与8051微控制器接口的硬件和软件设计实例。

MAX6902引脚配置
概述该应用笔记演示了MAX6902实时时钟与8051微控制器的接口方式，并提供了基本接口程序的例程。文中采用的微控制器为DS2250，软件用C语言编写。 工作原理该程序通过微控制器的四个通用端口控制SPI总线，微控制器向MAX6902发送一个控制/地址指令，启动数据传输；随后，微控制器向MAX6902发送其它数据或提供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

/***************************************************************************/
/* DEMO6902.c  This program is for example only and is not supported by    */
/*             Dallas Semiconductor Maxim                                  */
/***************************************************************************/
#include 		/* Register declaraTIons for DS5000 */
/***************************** Defines ********************************/
sbit CS      = P0^0;
sbit SCLK    = P0^1;
sbit DIN     = P0^2;
sbit DOUT     = P0^3;
/*********************** 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, CPOL = 1;

void set_spi()	/* ----- enable DUT with SCLK preset based upon CPOL ----- */
{
	if(CPOL)
	{
		CS    = 1;	/* make sure CS is high */
		SCLK  = 1;	/* set SCLK for CPOL=1 */
		CS    = 0;	/* enable DUT */
	}
	else
	{
		CS    = 1;	/* make sure CS is high */
		SCLK  = 0;	/* set SCLK for CPOL=0 */
		CS    = 0;	/* enable DUT */
	}
}
void reset_spi()	/* ----- reset DUT using SPI protocol ----- */
{
	if(CPOL)
	{
		CS    = 1;
		SCLK  = 1;
	}
	else
	{
		CS    = 1;
		SCLK  = 0;
	}
}
void wbyte_spi(uchar W_Byte)	/* ----- write one byte to DUT ----- */
{
uchar i;

	CS = 0;
	if(CPOL)
	{
		for(i = 0; i < 8; ++i)
		{
			DIN = 0;
			if(W_Byte & 0x80)
			{
				DIN = 1;
			}
			SCLK = 0;
			SCLK = 1;
			W_Byte <<= 1;
		}
	}
	else
	{
		for(i = 0; i < 8; ++i)
		{
			DIN = 0;
			if(W_Byte & 0x80)
			{
				DIN = 1;
			}
			SCLK = 1;
			SCLK = 0;
			W_Byte <<= 1;
		}
	}
}
uchar rbyte_spi(void)	/* ----- read one byte from DUT ----- */
{
uchar i;
uchar R_Byte;
uchar TmpByte;

	R_Byte = 0x00;
	DOUT = 1;	/* set up port for read */
	CS = 0;
	if(CPOL)
	{
		for(i=0; i<8; ++i)
		{
			SCLK = 0;
			TmpByte = (uchar)DOUT;
			SCLK = 1;
			R_Byte <<= 1;
			R_Byte |= TmpByte;
		}
	}
	else
	{
		for(i=0; i<8; ++i)
		{
		SCLK = 1;
		TmpByte = (uchar)DOUT;
		SCLK = 0;
		R_Byte <<= 1;
		R_Byte |= TmpByte;
		}
	}
	return R_Byte;
}
void writebyte()	/* ----- write one byte, prompt for address and data ------ */
{
uchar add;
uchar dat;
	/* Get Address & Data */
	printf("
Enter the Read Address
ADDRESS (1,2,3...):");
	scanf("%bx", &add);
	printf("
DATA (0-ff):");
	scanf("%bx", &dat);

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

	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);

	set_spi();
	wbyte_spi(0x3f);	/* clock burst write */
	wbyte_spi(sec);
	wbyte_spi(min);
	wbyte_spi(hr);
	wbyte_spi(dt);
	wbyte_spi(mn);
	wbyte_spi(dy);
	wbyte_spi(yr);
	wbyte_spi(0);		/* control */
	reset_spi();
	set_spi();
	wbyte_spi(0x13);
	wbyte_spi(0x20);	/* century data */
	reset_spi();
}
void disp_clk_regs()		/* --- loop reading clock, display when secs change --- */
{
uchar mil, pm, prv_sec = 99;

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

	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:
");

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

	set_spi();
	wbyte_spi(0x7f);	/* ram burst write */
	for (k=0; k < 31; k++)
	{
		wbyte_spi(Data);
	}
	reset_spi();
}
main (void)		/* ----------------------------------------------------- */
{
uchar i, M, M1;

	while (1)
	{
		printf("
MAX6902 build %s
", __DATE__);
		printf("CI. Initialize MAX6902
");
		printf("CW. Write Byte
");
		printf("CR. Read Time
");
		printf("RW. Write RAM
");
		printf("RR. Read RAM
");
		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;
		}
	}
}