AVR-Chat

I still think that you can do it without a crystal or other external
oscillator. You are going to have to use 2 pins for serial communication in
any case. I assume you want to talk to it in some way. Wake up your unit
with a few characters that you can measure the bit length like 5s or As or
whatever you pick, then set you bit time at what you find. Maybe that little
processor doesn't have enough memory for that sort of thing. But it is
totally doable to have a self adapting serial bit-bang type comm IO. You can
get it real close and each time it will figure out itself what is accurate
based on the input.

If you must have an external oscillator, I'd take Dave's advice. That
oscillator will probably work fine just as it is. The sine wave will also
most likely run the processor very well or as suggested you can square it up
but it may not be required. Important this is to try it and see what
happens.

Good luck,

Jim

----- Original Message ----- 
From: "Alexandre Guimaraes" <listas@logikos.com.br>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, July 05, 2005 1:07 PM
Subject: Re: [AVR-Chat] External oscillator for the Tiny13.


> Hi, James
>
>     The OSCCAL calibration works really very well if you can guarante the
> operating temperature.. If temperature varies too much it will not be
enough
> for reliable communications.. What makes the Tiny13 even more interesting
is
> that the voltage reference is much better than in the Atmega8, for example
> and the price tag is great for simple applications. It is small but for
some
> applications sparing a pin is possible..
>
>     The only other way that I can see to make reliable serial comms at
some
> speed with it is if we calibrate the timing using the timing of the start
> bit from the other serial device.. That works great but just under some
> protocols and it also makes software much more complicated..
>
>     If the external oscillator can be made cheaply enough it is a great
> option for many applications... The sub-dollar price tag with a nice AD
> converter and voltage reference that works makes the Tiny13 a very, very
> nice beast to be explored....
>
> Best regards,
> Alexandre Guimaraes
>
> ----- Original Message ----- 
> From: "James Hatley" <james.hatley@comcast.net>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Monday, July 04, 2005 11:47 PM
> Subject: Re: [AVR-Chat] External oscillator for the Tiny13.
>
>
> > Hello,
> >
> > Reviewing your original note ... you want to do serial communication and
> > you
> > think you need a crystal oscillator to clock the mpu.
> >
> > It seems to me that there is no reason that the internal oscillator and
a
> > bit-bang serial comm solution won't work just fine. These type of
routines
> > have been through here a number of times and I'm sure that there are a
> > number of examples around. The internal oscillator, at least in the
Atmel
> > mpus that I've used, can be tweeked with OSCCAL to get pretty close,
like
> > 2%
> > or better. That should be quite sufficient to do serial communication.
> >
> > That part, the ATtiny13 doesn't have too many pins and we don't know
what
> > you want to do but you may want/need to use the pin for something else.
> >
> > Jim
> >
> > ----- Original Message ----- 
> > From: Alexandre Guimaraes
> > To: AVR-Chat@yahoogroups.com
> > Sent: Monday, July 04, 2005 5:21 PM
> > Subject: [AVR-Chat] External oscillator for the Tiny13.
> >
> >
> > Hi,
> >
> >    All this talk about crystals got me thinking about a cheap way to
make
> > a
> > external oscillator for the Tiny13.... The only thing bad about this
part
> > is
> > that it can not drive a crystal to make serial comms possible :-(
Nothing
> > can be perfect....
> >
> >    Does anyone have a handy, small and cheap crystal oscillator circuit
> > that is reliable and uses low power ??? If it could use a resonator even
> > better.... It gets cheaper and is good enough for serial
communications...
> >
> > Best regards,
> > Alexandre Guimaraes
> >
> >
> >
> >
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