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Dear All:

I made a modification from FC example “Digital clock” to become a STOPWATCH (MM:SS:DD), but I tested this FC Stopwatch with a real Casio Stopwatch and they have about 10% different between 2 times, could you help me to check time interruption options or clock speed

Thanks

Hi armagon29.
You can try the following two thing to make your stop watch more accurate.

1) In your INITIALISE macro, Change prescaler in your timer interrupt from 1:1 to 1:256

2) In your INTERRUPT_TMR0 macro add a C Code box with at the beginning.


Let me know if that works please, and if it does I will explain what the problem was.
Your flowchart counts in 100th secs, secs and minutes now.

Martin

FC stopwatch works OK now

Thanks

Your welcome, Thanks for letting us know.
I will explain what was happening for anyone wishing to learn how the timer0 side works. Then it would be easier to create/alter flowcharts that involve timer0

For a brief explernaion of timer0 interrupt including why I added See:
http://www.matrixmultimedia.com/mmforum ... =26&t=8660

With the original digital clock example which I have attached, if you look at the timer0 properties In INITIALISE macro (double click or right click timer0 icon and select properties), the prescaler is set for 1:128 and below it shows interrupt frequency at 150Hz.
This means that the timer0 macro is accessed once every 1/150 = (6.667ms to 3 decimal places) = 150 times a second hence 150Hz
That is why in the SECONDS macro there is a decision branch , since 6.667ms x 150 = 1 second
So each time the SECONDS macro is accessed the SECOND_COUNTER is increased by 1, and when the value reaches 150, exactly a second has passed. The name SECOND_COUNTER is a bit missleading since when this value is increased by 1 its only 6.66ms has elapsed and not 1 second!

Going to the example armagon29 posted, is changed to .
Since this there is a calculation within the Yes part: then after timer0 interrupt is been accessed ONCE!this decision will then be true, both and will increase by +1. Looking at the timer0 properties interrupt frequency is 19200Hz this will happen every 1/19200 = 52us. Thats why the timing is out.

Here's what I did. I decided that the timer0 interrupt should trigger every 100ms since flowchart is created so 10 x increases

SECONDS_TENS

by 1, and 10 x increases Seconds by 1. Therefore since to get 1 scecond, the interrupt has to trigger 100 times. Since you want to LCD to display every 10ms like a stop watch, I have changed interrupt to the nearest lower value to 100Hz = 75Hz, and used my program posted here:
http://www.matrixmultimedia.com/mmforum ... =26&t=8660
To obtain desired value for .

Martin