MAX6900 RTC与8051位控制器的连接

摘要：本应用笔记提供了MAX6900 RTC与8051位控制器的硬件连接和软件例程。

说明

本应用笔迹介绍了MAX6900 I²C兼容RTC (实时时钟)与8051微控制器(µC)之间的连接方式，并提供了用于基本接口的程序代码。本范例中所使用的微控制器是DS2250, 软件用C语言编写。

操作过程

本程序利用作为I²C总线主机的微控制器的两个通用端口进行控制，MAX6900则作为同一总线上的从机器件。

电路原理图如图1所示，程序清单如图2所示。


放大图形
图1. 子卡原理图

图2. 程序清单

/***************************************************************************/
/* DEMO6900.c                                                              */
/***************************************************************************/
/* This program is for example only and is not supported by Dallas Maxim   */
#include 		/* Prototypes for I/O functions     */
#include 		/* Register declarations for DS5000 */
#define	ACK	0
#define	NACK	1
#define	ADD6900	0xa0	/* 2-wire addresses */
sbit scl = P0^0;        	/* 2-wire pin definitions  */
sbit sda = P0^1;
void	I2Cstart();
void	I2Cstop();
uchar	I2Cwrite(uchar);
unsigned char	I2Cread(int);
void	writebyte6900();
void	Initialize_MAX6900();
void	disp_clk_regs();
void	burstramread();
void	burstramwrt();
/* global variables */

void I2Cstart()		/* ----------------------------------------------- */
{
	sda = 1;	/* Initiate start condition */
	scl = 1;
	sda = 0;
}
void I2Cstop()		/* ----------------------------------------------- */
{
	sda = 0;	sda = 0;	/* Initiate stop condition */
	scl = 1;	scl = 1;
	sda = 1;
}
uchar I2Cwrite(uchar d)		/* ----------------------------- */
{
  int i;

  scl = 0;
	for (i = 0;i < 8; i++)
	{
		if (d & 0x80)
			sda = 1; /* Send the msbits first */
		else
			sda = 0;
		scl = 0;
		scl = 1;
		d = d < 1;	/* add to scl high time */
		scl = 0;
	}
	sda = 1;		/* Release the sda line */
	scl = 0;
	scl = 1;
	i = sda;
	scl = 0;
	if (i)
	{
		puts("Ack missing");
	}
	return(i);
}
uchar I2Cread(int b)	/* ----------------------------------- */
{
uchar i, d;

	d = 0;
	sda = 1;			/* Let go of sda line */
	for (i=1; i<=8; i++)		/* read the msb first */
	{
		scl = 0;
		scl = 1;
		d = d << 1;
		d = d | (unsigned char)sda;
	}
	scl = 0;
	sda = b;          /* Hold sda low for ACK, high for NACK */

	scl = 0;		/* toggle clock */
	scl = 1;
	scl = 0;

	sda = 1;		/* Release the sda line */
	return d;
}
void writebyte6900()	/* ----- write a single byte; user enters read address ----- */
{
uchar add;
uchar dat;
	/* Get Address & Data */
	printf("\nEnter the Read Address\nADDRESS (80,82,84...FC): ");
	scanf("%bx", &add);
	printf("DATA (0-ff):");
	scanf("%bx", &dat);

	I2Cstart();
	I2Cwrite(ADD6900);	/* slave address + write */
	I2Cwrite(add);
	I2Cwrite(dat);
	I2Cstop();
}
void Initialize_MAX6900()	/* ------- initialize from stdio entries ------- */
/* Note: NO error checking is done on the user entries! */
{
uchar	yr, mn, dt, dy, hr, min, sec, day;

	I2Cstart();
	I2Cwrite(ADD6900);		/* slave address + write */
	I2Cwrite(0x8e);		/* control register write address */
	I2Cwrite(0x00);		/* clear write protect */
	I2Cstop();

	printf("\nEnter 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);

	I2Cstart();
	I2Cwrite(ADD6900);	/* slave address + write */
	I2Cwrite(0xbe);	/* clock burst write */
	I2Cwrite(sec);
	I2Cwrite(min);
	I2Cwrite(hr);
	I2Cwrite(dt);
	I2Cwrite(mn);
	I2Cwrite(dy);
	I2Cwrite(yr);
	I2Cwrite(0);		/* control */
	I2Cstart();
	I2Cwrite(ADD6900);	/* slave address + write */
	I2Cwrite(0x92);
	I2Cwrite(0x20);	/* century data */
	I2Cstop();
}
void disp_clk_regs()		/* --------- display using burst mode --------- */
{
uchar Sec, prv_sec = 99, Min, Hrs, Dte, Mon, Day, Yr, cy;

while(!RI)	/* Read & Display Clock Registers */
{
	I2Cstart();
	I2Cwrite(ADD6900);		/* slave address + write */
	I2Cwrite(0xbf);		/* clock burst read */
	I2Cstart();
	I2Cwrite(ADD6900 + 1);	/* slave address + read */
	Sec = I2Cread(ACK);		/* starts w/last address stored in register pointer */
	Min = I2Cread(ACK);
	Hrs = I2Cread(ACK);
	Dte = I2Cread(ACK);
	Mon = I2Cread(ACK);
	Day = I2Cread(ACK);
	Yr  = I2Cread(ACK);
	cy  = I2Cread(NACK);		/* dummy read of control register */
	I2Cstart();
	I2Cwrite(ADD6900);		/* slave address + write */
	I2Cwrite(0x93);		/* century byte read address */
	I2Cstart();
	I2Cwrite(ADD6900 + 1);	/* slave address + read */
	cy  = I2Cread(NACK);
	I2Cstop();

	if(Sec != prv_sec)		/* display every time seconds change */
	{
		printf("\n%02bX%02bX/%02bX/%02bX %01bX", cy, Yr, Mon, Dte, Day);
		printf(" %02bX:%02bX:%02bX", Hrs, Min, Sec);
	}
	prv_sec = Sec;
}
   RI = 0;  /* Swallow keypress to exit loop */
}
void burstramread()		/* ----------------------------------------- */
{
uchar j, k;

	I2Cstart();
	I2Cwrite(ADD6900);	/* write slave address, write 6900 */
	I2Cwrite(0xff);	/* ram burst read */
	I2Cstart();
	I2Cwrite(ADD6900 + 1);	/* slave address + read */
	printf("\nRAM contents");
      for (j=0; j<30; ++j)
	{
		if(!(j % 8) )	printf("\n");
		printf("%2.bX ", I2Cread(ACK) );
	}
	printf("%2bX", I2Cread(NACK) );	/* last byte, NACK */
	I2Cstop();
	printf("\n");
}
void burstramwrt(uchar Data)		/* ----------------------------------------- */
{
uchar j, k;

	I2Cstart();
	I2Cwrite(ADD6900);	/* write slave address, write 6900 */
	I2Cwrite(0xfe);	/* ram burst write */
	for (k=0; k < 31; ++k)
	{
		I2Cwrite(Data);
	}
	I2Cstop();
}
main (void)		/* ----------------------------------------------------- */
{
uchar i, M, M1;

	while (1)
	{ 
		printf("\nMAX6900 build %s\n", __DATE__);
		printf("CI Clock Init\n");
		printf("CR Clock Read BW Byte Write\n");
		printf("RR RAM Read   RW RAM Write\n");
		printf("Enter Menu Selection: ");

		M = _getkey();

		switch(M) 
		{
			case 'B':
			case 'b':
			printf("\rByte: B");
			M1 = _getkey();

			switch(M1) 
			{
				case 'W':
				case 'w':	writebyte6900(); 
						break;
			}	break;

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

			switch(M1) 
			{
				case 'I':
				case 'i':	Initialize_MAX6900();
						break;

				case 'R':
				case 'r':	disp_clk_regs();
					      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("\nEnter the data to write: ");
						scanf("%bx", &i);
						burstramwrt(i);	break;
			}	break;
		}
	}
}