question about digital clock project posted here.

[romel emperado]

guys pls explain to me how did they come up with this calculation for the timer to generate a delay of 1sec..

 

 

this project is posted here: http://www.engineersgarage.com/microcontroller/8051projects/digital-clock-AT89C51-circuit

void delay()        //Function to provide a time delay of approx. 1 second. using Timer 1.

{

int i;

for(i=0;i<20;i++)

{

TL1=0xFD;

TH1=0x4B;

TR1=1;

while(TF1==0);

TR1=0;

TF1=0;

}

}

FD4B is 64843 in decimal  so pls tell me how would that calculation genarate 1 second? that is less that a second.. correct me IF am wrong but i think something wrong with the calculation..

 

 

I have my own code here to generate 1second using 12Mhz crystal but i dont get it how the above code geraate a second delay..

 

 

void delay(char k)
{
  char i;
  TR1=0;
  for(i=0; i<k; i++)
  {
    TH1=0x3c;
    TL1=0xB0;
    TF1=0;
    TR1=1;
    while(TF1==0);
    TR1=0;
  }
}

[dagakshay]

hello romel,

 

How does the code you have pased above (which which given on site) is giving 1 second…

 

timer register is a 16 bit register since they are using it in mode1

 

TH1=0x4B;

TL1=0xFD;

 

so 4BFD = 19453 in decimal

 

65535 – 19453 = 46083;

 

they using 12MHz crystal so freq./12clock

12MH/12=1Mhz

t=1/f=1 us in the case of 12 MHz crystal

if they would have used 11.0592 Mhz it would be 1.085 us

 

46083*1us*20 loops= 921660 us near about 0.92 second for 12Mhz

46083*1.085us*20 loops= 1000001.1 micro second which is more closer to 1 second

 

ideally they would have used or calculated it for 11.0592Mhz

 

and the delay function(second one) which you have pasted will count = 49999 us*k (according to 12Mhz)

if k=20 the total it will give around 0.99 second… so you delay in case of 12 Mhz will be more accurate..

[romel emperado]

haha look at my previous post… My convertion is wrong that is why i said it’s less than a second.. hehe thanks so much yar

[romel emperado]

hello again.. i have done actual hardware experiment about the accuracy of these values and i come up results.

 

 

this value below is not realy accurate 1 second delay. i compared it to a real digital clock it will be late for 20secs after 48hours..

 

TH1=0x3C;

TL1=0xB0;

 

i think this one would be better but its under observation

 

TH1=0x3C;

TL1=0xBB;

 

its beter to use RTC… less hassle .. hihi

[dagakshay]

it is delayed because the crystal we use that is why for higher research ppl generally you other clock source… exaclty i dont remember what is that term… “partially it is an atomic clock” which basically some of relation with the nuclear half life period i dont know its complete details…in the case of watch for more acuracy analog clock are prefered rather then the digital one… you yourself can see the difference.. buy a local digial clock and a standard one any branded digital clock… set them with same time just in few months you can notice the dealy b/w them.. that is why standard companies digital clock are more costaly than the local one… its a very nice concept i read a long back thanks for repolishing my old dead blocks… i will surly write an artical on it and send it to you as soon as possible…..

[romel emperado]

yeah thanks for answering yar.. yes it is true…

 

but for some hobbyist in embedded system using real time clock(RTC) and interface with controller is much better compared of using timer interrupt..

 

example of RTC use in some projects is DS 1307..

[dagakshay]

Interfacing RTC again makes the ckt bulier and the code goes heavier… you can use the controller which would hae inbult RTC… but again id depends on kind of application you using… sor some small applications timer is more than sufficient

[romel emperado]

I agree.. it depends on your application..

 

 

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