Timer2 question

[jseidmann]

Hello All,

i'm using a PIC16F876 and I have a question about using Timer2 as an interrupt. I'm trying to understand how to figure out when the interrupt occurs and when it resets and what is the difference between the two? Currently I have timer2 settings as:


setup_timer_2(T2_DIV_BY_16, 156,1)
and its running at 20MHz

I believe that the T2_DIV_BY_16 is a prescalar to take it from 20MHz to (20/16)MHz, but what does the 156 mean and what does the 1 mean? ANy help would be so unbelieveably greatly appreciated.

Jon

[jseidmann]

Also, what would happen if I changed the '1' to a '2'?

thanks

[dyeatman]

Syntax:
setup_timer_2 (mode, period, postscale)

Parameters:
mode may be one of:

T2_DISABLED, T2_DIV_BY_1, T2_DIV_BY_4, T2_DIV_BY_16

period is a int 0-255 that determines when the clock value is reset,

postscale is a number 1-16 that determines how many timer resets before an interrupt: (1 means one reset, 2 means 2, and so on).

Function:
Initializes timer 2. The mode specifies the clock divisor (from the oscillator clock). The timer value may be read and written to using GET_TIMER2() and SET_TIMER2(). Timer 2 is a 8 bit counter/timer.

Requires
Constants are defined in the devices .h file.

Examples:
setup_timer_2 ( T2_DIV_BY_4, 0xc0, 2);

// At 20mhz, the timer will include every 800ns,

// will overflow every 153.6us,

// and will interrupt every 460.3us.

[rnielsen]

Sometimes the manual/'help file' is a bit hard to understand for somebody that's not experienced the PIC very much.

[jseidmann]

thank you, that is very clear. I had already looked at the manual and it didnt mention the timer clock being 1/4th the oscillator or really flesh out the details. I appreciate all your help.

jon