[SOLVED] 8051 Timer Programming.

[Titus Manoj Kumar]

Dear All,

Am working on 8051 timer programming. I have a doubt in that,

TH0 = 0xFC;
TL0 = 0x66;

Here as we know the Timer 0 reg.is assigned a hex value of FC66.

This one is said to be the estimated value for 1ms delay.

How do we calculate the time with regards to hex values.?

Please help.
Thanks.

 

[KlausST]

Hi,

usually the descripton of the timer functions you can find in the datasheet.


if you need to calculate hex to decimal and back, look for online calculators.


Klaus

 

[bassa]

Manoj,

Can you specify the timer mode which you are using for this and crystal frequency

Also refer these

**broken link removed**

Google search for "calculator for 8051 family by kaushik". This simple program you can generate 8051 code

bassa

 

[Titus Manoj Kumar]

Baasa,

Timer Mode is Mode1.

freq : 11.0592Mhz.

 

[bassa]

Check this tool for result.



Details:

Timer mode 1 = 16 bit timer and timer will overflow @ FFFF+1 (65535+1)
Your timer value = FC66

Total machine cycles need to overflow = FFFF+1 - FC66 = 039A ( 65536 - 64614 = 922)
Total time = Total machine cycles need to overflow * machine cycle time = 922*1.085 = 1000us = 1ms

bassa

 

[Titus Manoj Kumar]

Baasa,

Thanks much for the help.

I need to control a DC Motor with a period of 3 minutes. So whats the xtal frequency should I use? and what are the values should i load into TH0 and TL0 registers?

 

[Titus Manoj Kumar]

8051 Timer Functions.

Dear all,

I need to control a DC Motor with a period of 3 minutes using timer function.

So whats the xtal frequency should I use?

And what are the values should i load into TH0 and TL0 registers?

Please do help.

Thanks.

 

[bassa]

Baasa,

I need to control a DC Motor with a period of 3 minutes. So whats the xtal frequency should I use? and what are the values should i load into TH0 and TL0 registers?

To reduce error, it is better to use 12MHz xtal frequency.

There are many ways to generate 3 minutes time delay, configure the timer to 50ms and loop 3600 (20*60*3) times or use software delay loops or find out RTC

 

[th3gr8]

Re: 8051 Timer Functions.

You can use any xtal but keep in mind that the xtal value will affect the delay ..
8051's instruction cycle time is = Xtal_Frequency / 12 .. So if you use 12Mhz it will make the calculations a bit easier .. Another commonly Xtal value used is 11.0592 Mhz because it is useful when you use serial communication ..
Now, for your delay of 3 minutes, you can do it in many ways .. You can make a delay of 1sec and call it 180 times (by using for loop) ..

 

[KlausST]

Hi,

You need us to calculate for you how many ms in 3 minutes are?

Klaus

- - - Updated - - -

Hi,

To reduce error, it is better to use 12MHz xtal frequency.

Mathematically this is true. True if you want to program a software clock.

But if the value for the timer setup is about 50000 then the estimated error is max. +/- 0.5/50000.
This is about +/- 10 ppm. That is in the range of the quartz frequency tolerance.

The max error with 3 minutes is at about +/- 1ms.
I am very sure that this error should give no problem with controlling a dc motor.

Klaus

 

[Disha Karnataki]

So whats the xtal frequency should I use?

And what are the values should i load into TH0 and TL0 registers?

xtal frequency is always fixed i.e. 11.0592MHZ crystal.
now if you want 3 second delay as the timers delay support max delay of 71.111ms so you will have to loop the timer.
so let us take (50ms delay & loop it 60 times)together 60times again it will give you 3min delay
calculations:
65535-required value loaded in THTL+1=50millsec/1.085microsec (i hope you know this formula)
required value to be loaded in hex is:
TH VALUE:4Ch
TL VALUE:00h
first of all whether you want it to be written in c or asm?

in asm language delay subroutine

mov tmod,#01h
mov r1,#60
up1:mov r0,#60    //counter to repeat 50ms for 60 times
up:
mov th0,#4ch
mov tl0,#00h
setb tr0  //start timer
here:jnb tf0,here      //wait till timer flag raised
clr tf0
clr tr0
djnz r0,up
djnz r1,up1
ret

in c :

{
unsigned int y,x;
TMOD=0X01;   //timer0 mode 1
for(y=0;y<=60;y++)
{
for(x=0;x<60;x++)
{
   TH0=0X4C;
TL0=0X00;
TR0=1;
while(TF0==0);      //wait till overflow flag raised
TR0=0;
TF0=0;
}

see atlast o/p in logic analyser of your compiler to verify

 

[KlausST]

Hi,

so let us take 50ms delay & loop it 60 times it will give you 3min delay

please re-calculate this, otherwise it may confuse the OP.


Klaus

 

[Disha Karnataki]

you can see it i have edited

 

[Titus Manoj Kumar]

Thank u so much Disha Karnataki.