Timers on the PIC

[Kevin Mayer]

Alright - I'm getting the hang of things now - but I'm not 100\% sure about the timer operations.

- Is it correct to say that all the timers (I'm using the PIC16F877) tick once over (4/clock rate) seconds? (if so, why '4'?)

- What is the deal with internal or external clock (eg., T1_INTERNAL, T1_EXTERNAL, T1_EXTERNAL_SYNC) - do the timers not necessarily go off the clock input I have hooked up to the chip?

Cheers :-)
Kevin
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This message was ported from CCS's old forum
Original Post ID: 1438

[ajt]

:=Alright - I'm getting the hang of things now - but I'm not 100\% sure about the timer operations.
:=
:=- Is it correct to say that all the timers (I'm using the PIC16F877) tick once over (4/clock rate) seconds? (if so, why '4'?)

Yes, unless you use a prescaler or postscaler. The reason for 4 is that the processor executes an instruction in one CPU cycle (except jumps which take 2 cycles) and 1 cycle of the CPU takes four oscillator clock ticks. The Timers "clock" on instruction cycles.

:=
:=- What is the deal with internal or external clock (eg., T1_INTERNAL, T1_EXTERNAL, T1_EXTERNAL_SYNC) - do the timers not necessarily go off the clock input I have hooked up to the chip?

Timer0 and Timer1 can be clocked from an external source using a PORTA or PORTC pin, respectively.

:=
:=Cheers <img src="http://www.ccsinfo.com/pix/forum/disagree.gif" border="0">)
:=Kevin
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This message was ported from CCS's old forum
Original Post ID: 1441
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Al Testani

[Kevin Mayer]

THANKS :-)
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This message was ported from CCS's old forum
Original Post ID: 1443