16 bit timer

[2camjohn]

I moved some of my routines from an 8 bit timer to the 16 bit timer on the 16f819.

From my understanding the timer works exactly the same except it overflows after 65536 ticks instead of 256.


So I expected to see the routine slow down alot (with the same prescalar it should run 256 times slower than an 8 bit timer). But it doesnt.

Am I misunderstanding how 16 bit timers work(I thought it just had to count upto 16 bits instead of 8 )?

Is there anything else I should know?


Cheers
John

 

[Pommie]

The 16 bit timers don't use the prescaller in the OPTION register. Timer 1 and 2 have there own prescallers.

Mike.

 

[2camjohn]

I have the prescalar currently set to

T1CON.T1CKPS1 = 1
T1CON.T1CKPS0 = 1

Thats from the timer1 section of the datasheet.
But it seems to go as fast as the 8 bit timer!!!

Just to confirm a 16 bit timer will only create an overflow once it has incremented 65536 times???



Cheers
John

 

[Pommie]

Just to confirm a 16 bit timer will only create an overflow once it has incremented 65536 times???

Cheers
John

Yes, in your case, with the prescaler set to 8, it will be 8*65536.

How are you testing for overflow? With TMR1IF?

Mike.

 

[2camjohn]

Yes

And it is reset to zero at the end of the timer routine.



Thanks for the help so far...

John