Time measuring with 16f877

[PIC2PIC]

Hi

I made a device that counts the time, something like a clock. And I use Watch Dog Timer to count seconds.But the problem is accuracy, i.e. for every minute my clock is fast about 1 second.

I use PIC 16f877.

So I have 2 questions:

1. Is there a better and more accurate way to count seconds or smaler fractions of seconds then to use WDT
2. In assembly code I try to improve accuracy in every minute by substracting one second after every 61
"Seconds" ,but strange thing happen. I regulate memory bank for each register, but in a
dissassembly listing in MPLAB is shown that the address of the memory register that I use is some other bank
diferent then I set, and that means some other memory register, and I can't do nothing to change that .
What could be reason for this?

 

[ericgibbs]

hi,
Use Timer1 for your 'timed' interrupt, not the WD timer.

Whats the crystal frequency.?

 

[Nigel Goodwin]

1. Is there a better and more accurate way to count seconds or smaler fractions of seconds then to use WDT

There's no worse way - it will make an absolutely terrible clock, and isn't intended to be used in that way - the clue is in it's name.

 

[PIC2PIC]

Thank you for answering.

My crystal frequency is 4MHz.

 

[blueroomelectronics]

Some good reading for a zero error 1 second clock when using a 4MHz crystal.
Zero-error 1 second timing algorithm
**broken link removed**