MAX6900 RTC与8051位控制器的连接

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。


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 AddressnADDRESS (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 %sn", __DATE__);

printf("CI Clock Initn");

printf("CR Clock Read BW Byte Writen");

printf("RR RAM Read   RW RAM Writen");

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;

}

}

}