calcule tmr0

[brunosilva]

I wonder how and performed the calculation of the timer
I am using an example of the matrix.

TMR0
select clock source: internal clock (CLKO)
source edge select: high-to-low transitionn on TMR0 clock

1:8 prescaler rate

outcome and

8000000hz
976 563 hz frequency

I want to know how and made ​​the calculation.

And how do the LED flashes 2 seconds for the calculation to get it

[saschech@gmx.de]

Hello

have a look to a calculator.....
http://www.libstock.com/projects/view/3 ... calculator

Regards wolfgang

[medelec35]

Hi brunosilva

This is how I calculate Interrupt frequency:

1/((256-timer offset)*Prescaler Rate/(Clock Frequency/4))

=1/((256-0)*8/(8000000/4))

1/0.001024
= 976.5625Hz

This means that interrupt macro is accessed 976 times every second.
So if you use a integer variable called Count and you want to flash a LED connected to Porta0
Then within interrupt do:
Count = count + 1

If Count >= 1952 then Count = 0: LED_ON=!LED_ON :PortA0 LED_ON

LED_ON is a variable for sending to the port PortA0 output component macro
That should make LED change state every 2 seconds.

Note the timer offset is use to speed timer interrupt up
Timer interrupt triggers when internal register rolls over i.e 254,255,rolls over to 0
If tmr0 is assigned with a number (e.g 100) at the beginning of interrupt macro, then since after rollover instead of counting from 255,0,1,2 etc, it will go 255,0,100,101 etc
Hence rolls over quicker so interrupt frequency is increased.
If this offset is not used then a 0 is used in the calculation.

Try creating a flowchart with the above information to flash LED every two seconds.

If you get stuck then post what you have done so far, and I will take a look at it.

Also please don't double post with the same question.


Martin

[brunosilva]

When I know when I'm using a timer 8-bit and 16-bit

how do the calculation to get 3 seguindos in 16-bit

how do i get 3/2 with 8 bits.

cycle machine * preescaler * (so 8/16 - count value of timer 0)

3 000 000 = 0.5 * 128 * (65536 - x)

X = 65536-46875
x = 18661

How to do this using Flowcode without using code c

And if they give me a default value of 976 per second can I have only one I'm checking the examples of matrix but I'm still having trouble

to understand how and held the timer

Thank you

[medelec35]

Hi brunosilva
Sorry not got time this morning to answer properly.
Take a look at this post:
http://www.matrixmultimedia.com/mmforum ... 14&#p18514
Which should help set your flowchart up to change LED pattern every second.

You may find it better explaining in your native language.

[brunosilva]

I do not understand this calculation timer 0.
In this case he is using a 4 MHz clock that will generate him a time
61,035 hz and also has a delay in the program what it does?

then if it has a <61 seems more time passes than 1 second.

Its help me in my code below.

Sorry for the inconvenience could not understand right that part of TMR0.

thank you

[medelec35]

The delay has not nothing to do with timer0 interrupt, it#s there to prevent issues if component macros are access too fast.
I just chose a random delay time.
So you can forget the delay for calculating interrupt times since interrupt times will stay the same not matter what the delay time is.
In your case it may work just fine without.

If it was me, I would want interrupt running as slow as possible.
So as explained in the link posted choose a prescaler rate of 1:128 since that will produce the lowest interrupt frequency(61.035HZ) that can be rounded to a whole number.
i.e its better to use 61.035 than 31.518 (prescaler rate 1:256)
Reason 1st one is only 0.035 away from a whole number.
Whereas second one is 0.518 away from 31 or 0.482 away from 32 so with both of these there will be higher timing errors.
I have adjusted flowchart with recommended interrupt settings for one second timing, but used the 1:128 which will be better.
The faster the interrupt is serviced then less time is available for the rest of your program.
So use the slowest interrupt time as possible.
If not you will face hardware issues.

Note: Simulation will take much longer that hardware.

Also if using a value higher than 255 e.g
If int_count < 976
Then you MUST use integer type and not byte type since bytes only go from 0 to 255
So if you change int_count from a byte to and integer in the flowchart you posted, that should also work.

[brunosilva]

Thanks for the trouble

I understand now how the timer

[brunosilva]

one doubts

can I have five minutes timer 0?

thank you

[medelec35]

Hi brunosilva,
You can try attached Flowchart.

Note: Clock speed is set for 8MHz which is what you stated in your first post.
If your using a different crystal (or resonator) then you will need to alter interrupt and count settings.

Best crystal or resonator for the job is a standard 19660800Hz (19.660800MHz)
Reason is because it allows more accurate timing when dividing down.
E.g You can select interrupt frequency of 75.000Hz, 150.000Hz, 300.000Hz etc.

[brunosilva]

thank you

If I want to use 5/2 and so make him repeat 5 times in the right program?

How do I work with the timer counter 0 as

I am not able to create a program that when I precionar the button 5 times turns on a led using timer 0

Thanks for the trouble