> Yes.  And I've noticed that of 2 app notes I found that use/set TMR1,
> neither are switching it off before writing.  Yet they claim to be
> "real-time" apps.

Don't look to the app notes for examples of well written code.  I've seen
too much bad coding to trust any of them.  Personally, I think they are a
waste of time at best, downright misleading at worst.

> I'm planning to try their technique just to see what
> type of timing it gives me.

That won't prove anything.  The problem is subtle and small, so it may not
occur, or you may not notice if it does occur a few times.  Eventually it
may cause long term time drift.  Trust the data sheet, ignore the app
notes.

> IIRC, one is writing 0x80 to TMR1H for
> 1-sec interrupts, but they do it a few instructions into the ISR.  I
> can see that if done only a few instructions into the ISR, writing to
> the hi-byte only cannot really mess up the counter pair since it should
> be at zero all during this time, but what about the prescaler?

It *might* be OK to write the high byte when you know a carry from the low
byte can't happen.  However, the data sheet is unclear on this, and I
wouldn't count on it.


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