[51] rtc ds1307 with 8051 can't update date & time after mains power switch on

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aviraje8

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here is the code
when power on the system it start displaying date & time,but when I turns power off then again turn on the power it displays initial value not updated value



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#include<reg51.h>
 
void _nop_(void);
 
#define delay_us _nop_(); //generates 1 microsecond
 
#define LCD P0
 
sbit RS=P2^0; 
 
sbit EN=P2^1; 
 
sbit SCK=P2^3; //serial clock pin
 
sbit SDA=P2^4; //serial data pin
 
 
#define SCKHIGH  SCK=1;
 
#define SCKLOW   SCK=0;
 
#define SDAHIGH  SDA=1;
 
#define SDALOW   SDA=0;
 
 
void integer_lcd(int);
 
void init_lcd(void);
 
void cmd_lcd(unsigned char);
 
void write_lcd(unsigned char);
 
void display_lcd(unsigned char *);
 
void delay_ms(unsigned int);
 
void SDelay_ms(unsigned int);
void MDelay_ms(unsigned int);
void T0Delay(void);
 
void start(void);
 
void stop(void);
 
void send_byte(unsigned char);
 
unsigned char receive_byte(unsigned char);
 
void write_i2c(unsigned char,unsigned char,unsigned char);
 
unsigned char read_i2c(unsigned char,unsigned char);
 
 
void sys_init(void);
 
//clock[]={seconds,minutes,hours,day_of_week,date,month,year};
 
unsigned char clock[]={0x00,0x59,0x23,0x02,0x31,0x12,0x15};
 
unsigned char *s[]={"SUN","MON","TUE","WED","THU","FRI","SAT"};
 
unsigned char slave_ack,add=0,c,k,p,q,r,t,u,v;
 
unsigned int num,m;
        
            // Real Time Clock Mode
 
void main(void)
{
init_lcd();
 
 
while(add<=6)   //update real time clock
 
                        {
 
                        write_i2c(0xd0,add,clock[add]);
 
                        add++;
 
                        }
 
 
         sys_init();
 
           
}
 
void sys_init()
 {  
      
 
while(1)
{
                       p=read_i2c(0xd0,0x02);//read hours register and display on LCD
 
                        write_lcd((p/16)+48);
 
                        write_lcd((p%16)+48);
 
                        write_lcd(':');
 
                       
                        q=read_i2c(0xd0,0x01);//read minutes register and display on LCD
 
                        write_lcd((q/16)+48);
 
                        write_lcd((q%16)+48);
 
                        write_lcd(':');
 
                         
                        delay_ms(10);
 
                        r=read_i2c(0xd0,0x00);//read seconds register and display on LCD
 
                        write_lcd((r/16)+48);
 
                        write_lcd((r%16)+48);
 
                        write_lcd(' ');
 
                       
                        display_lcd(s[read_i2c(0xd0,0x03)]);//read day register and display
                       
 
                        cmd_lcd(0xc0);
 
                        t=read_i2c(0xd0,0x04);//read date register and display on LCD
 
                        write_lcd((t/16)+48);
 
                        write_lcd((t%16)+48);
 
                        write_lcd('/');
                      
 
                        u=read_i2c(0xd0,0x05);//read month register and display on LCD
 
                        write_lcd((u/16)+48);
 
                        write_lcd((u%16)+48);
 
                        write_lcd('/');
 
                       
                        write_lcd('2');
 
                        write_lcd('0');
 
                        v=read_i2c(0xd0,0x06);//read year register and display on LCD
 
                        write_lcd((v/16)+48);
 
                        write_lcd((v%16)+48);
                       
 
                        delay_ms(100);
 
                        cmd_lcd(0x01);
 
                        if(p>=23 && q>=0x59 && r>=0x59 && t>=31 && u>=12 && v>=15)
                        {
                        delay_ms(100);
                        P1=0X00;
                        }
 
}                            
                                             
 }
 
                     
//starts i2c, if both SCK & SDA are idle
 
void start(void)
 
{ 
 
            if(SCK==0) //check SCK. if SCK busy, return else SCK idle
 
                        return;
 
            if(SDA==0) //check SDA. if SDA busy, return else SDA idle
 
                        return;
 
SDALOW //data low
 
delay_us
 
SCKLOW  //clock low   
 
delay_us
 
}          
 
//stops i2c, releasing the bus
 
void stop(void)
 
{        
 
SDALOW //data low
 
SCKHIGH //clock high
 
delay_us
 
SDAHIGH //data high
 
delay_us
 
}
 
 
//transmits one byte of data to i2c bus
 
void send_byte(unsigned char c)
 
{
 
unsigned mask=0x80;
 
            do  //transmits 8 bits
 
            {
 
                        if(c&mask) //set data line accordingly(0 or 1)
 
                                    SDAHIGH //data high
 
                        else
 
                                    SDALOW //data low
 
                        SCKHIGH   //clock high
 
                        delay_us
 
                        SCKLOW   //clock low
 
                        delay_us
 
                        mask/=2;  //shift mask
 
            }while(mask>0);
 
SDAHIGH  //release data line for acknowledge
 
SCKHIGH  //send clock for acknowledge
 
delay_us
 
slave_ack=SDA; //read data pin for acknowledge
 
SCKLOW  //clock low
 
delay_us
 
}      
 
 
 
//receives one byte of data from i2c bus
 
unsigned char receive_byte(unsigned char master_ack)
 
{
 
unsigned char c=0,mask=0x80;
 
            do  //receive 8 bits
 
            {
 
                        SCKHIGH //clock high
 
                        delay_us
 
                                    if(SDA==1) //read data
 
                                                c|=mask;  //store data
 
                        SCKLOW  //clock low
 
                        delay_us
 
                        mask/=2; //shift mask
 
            }while(mask>0);
 
            if(master_ack==1)
 
                        SDAHIGH //don't acknowledge
 
            else
 
                        SDALOW //acknowledge
 
SCKHIGH //clock high
 
delay_us
 
SCKLOW //clock low
 
delay_us
 
SDAHIGH //data high
 
return c;
 
}
 
 
 
 
 
 
 
//writes one byte of data(c) to slave device(device_id) at given address(location)
 
void write_i2c(unsigned char device_id,unsigned char location,unsigned char c)
 
{
 
            do
 
            {
 
                        start();      //starts i2c bus
 
                        send_byte(device_id); //select slave device
 
                        if(slave_ack==1)  //if acknowledge not received, stop i2c bus
 
                                    stop();
 
            }while(slave_ack==1); //loop until acknowledge is received
 
send_byte(location); //send address location
 
send_byte(c); //send data to i2c bus
 
stop(); //stop i2c bus
 
delay_ms(4);
 
}      
 
 
 
//reads one byte of data(c) from slave device(device_id) at given address(location)
 
unsigned char read_i2c(unsigned char device_id,unsigned char location)
 
{
 
unsigned char c;
 
            do
 
            {
 
                        start();   //starts i2c bus  
 
                        send_byte(device_id); //select slave device
 
                        if(slave_ack==1) //if acknowledge not received, stop i2c bus
 
                                    stop();
 
            }while(slave_ack==1); //loop until acknowledge is received
 
send_byte(location);  //send address location     
 
stop(); //stop i2c bus
 
start(); //starts i2c bus  
 
send_byte(device_id+1); //select slave device in read mode
 
c=receive_byte(1); //receive data from i2c bus
 
stop(); //stop i2c bus
 
return c;
 
}      
 
 
 
/*display of 16bit(integers) values on LCD
 
void integer_lcd(int n)
 
{
 
unsigned char c[6];
 
unsigned int i=0;
 
  if(n<0)
 
  {
 
    write_lcd('-');
 
    n=-n;
 
  }
 
  if(n==0)
 
    write_lcd('0');
 
  while(n>0)//Split integer to 2 bytes and send on 8bit line.
 
  {
 
    c[i++]=(n%10)+48;
 
    n/=10;
 
  }
 
  while(i-->=1)
 
    write_lcd(c[i]);
 
}*/
 
 
 
//initialize lcd
 
void init_lcd(void)
 
{                           
 
delay_ms(10); //delay 10 milliseconds
 
cmd_lcd(0x0e); //lcd on, cursor on
 
delay_ms(10);
 
cmd_lcd(0x38); //8 bit initialize, 5x7 character font, 16x2 display
 
delay_ms(10);
 
cmd_lcd(0x06); //right shift cursor automatically after each character is displayed
 
delay_ms(10);
 
cmd_lcd(0x01); //clear lcd
 
delay_ms(10);
 
cmd_lcd (0x80);
 
}
 
 
 
//transmit command or instruction to lcd
 
void cmd_lcd(unsigned char c)
 
{
 
EN=1;
 
RS=0; //clear register select pin
 
LCD=c; //load 8 bit data
 
EN=0; //clear enable pin
 
delay_ms(2); //delay 2 milliseconds
 
}
 
 
 
//transmit a character to be displayed on lcd
 
void write_lcd(unsigned char c)
 
{
 
EN=1; //set enable pin
 
RS=1; //set register select pin
 
LCD=c;  //load 8 bit data
 
EN=0; //clear enable pin
 
delay_ms(2); //delay 2 milliseconds           
 
}
 
 
 
//transmit a string to be displayed on lcd
 
void display_lcd(unsigned char *s)
 
{
 
while(*s)
 
write_lcd(*s++);
 
}
 
 
 
//generates delay in milli seconds
 
void delay_ms(unsigned int i)
 
{
 
unsigned int j;
 
            while(i-->0)
 
            {
 
                        for(j=0;j<500;j++)
 
                        {
 
                                    ;
 
                        }
 
            }
 
} 
 
void T0Delay()
{
TMOD=0X50;
TL0=0XB0;
TH0=0X3C;
TR0=1;
while(TF0==0);
TR0=0;
TF0=0;
}
 
void MDelay_ms(unsigned int i)
{
unsigned int j;
while(i-->0)
{
for(j=0;j<7000;j++)
{
    ;
}
}
}
 
void SDelay_ms(unsigned int m)
{
unsigned int z;
 m=m*200;
 
for(z=0;z<=m;z++)
{
T0Delay();
}
}
 
Last edited by a moderator:

if it is loosing information when the power is removed have you checked the backup battery circuit is operating correctly?

does the SRAM loose data s well?
 

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