Re: 9V AC needed for C64?

From: Cameron Kaiser (
Date: 1998-09-03 18:46:22

>Well, that won't cause any problems -- the CIA timer (the interrupt timer)
>runs in continuous mode.  So although there might be some little fluctuations,
>after 1000 interrupts the TI$ counters will have been incremented 1000 times.
>(Kind of like the way the AC line is only 60Hz or 50Hz on average).  On the
>other hand, I think the tape routines change the IRQ vector, and of
>course anything that changes the timer value or skips the update will
>mess up the clock.

Tape definitely does dork with the IRQ vector.

>Let's see now... the interrupt timer uses a latch value of 17045.  This 
>means an interrupt takes place every
>	17046 cycles * 14/14318181 sec/cycle = 0.0166672 seconds
        ^^^^^ ?

Just a typo?

>So, TI seems to stay pretty accurate (I always had it in my head that
>it wasn't).

TI$ is really easy to use, also. The TOD's latching makes things a little
tricky -- and Jim Butterfield has mentioned how perverse setting it can be.
I'm lazy, on top of all that.

Cameron Kaiser *** ***
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