Could it be as simple as:
One timer period on, one period off?
That would divide your 15 Hz  down to 7.5.
And then there is the timer prescaller...

Rodrigo Valladares P wrote:

>Hi all.
>
>i have a little circuit that i expect a 15 hz cycle, but it oscillate at 
>about 3hz (eye-measured)
>
>fosc = 4MHz (internal oscillator) so,
>fosc / 4 = 1MHz
>1MHz / 65536 = 15hz
>
>what is wrong?, this is my first interrup circuit :( is fosc really 4 
>MHz / 4 / 4 ??
>
>thanks in advance
>
>RVP
>
>this is a mikrobasic code
>
>dim counter as byte
>
>sub procedure interrupt
>    if PIR1.TMR1IF <> 0 then
>     inc(counter)
>     PIR1.TMR1IF = 0
>   end if
>end sub
> 
>main:
>
>  while TRUE            ' Endless loop
>    TRISB = 0           ' Configure pins of PORTB as output
>    counter = 0 '
>   
>  INTCON = 0
>
>  T1CON.T1CKPS1 = 0
>  T1CON.T1CKPS0 = 0 ' preescaler 1:1
>
>  T1CON.T1OSCEN = 0 ' osc shut down
>  T1CON.NOT_T1SYNC = 1 ' not needed?
>
>  T1CON.TMR1CS = 0 ' internal clock fosc/4
>  T1CON.TMR1ON = 1 ' enable timer
>
>  PIE1.TMR1IE = 1 ' enable overflow interrupt
>
>  INTCON.PEIE = 1 ' enable peripheral interrupt
>  INTCON.GIE = 1 ' enable global interrupt
>
>    while true
>
>      PORTB = counter
>
>    wend
>  wend
>
>
>
>
>
>  
>

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  |  __O    Thomas C. Sefranek   WA1RHP@ARRL.net
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