AVR-Chat

Wait.... What?

"There are fuse settings, however, to run with an external clock signal,
in which case, unless you have an external clock attached you will lose
the ability to reprogram the chip after you make that change."

Are you saying that if I use an external clock I can't upload the flash
anymore?  I hope not.

I'll be using an external crystal and perhaps an external clock chip.
I'll need some accuracy because this device is used for timing
applications up to about 80 seconds.

Barry


-----Original Message-----
From: Brian Dean [mailto:bsd@bdmicro.com] 
Sent: Sunday, March 28, 2004 6:57 AM
Subject: Re: [AVR-Chat] Re: start AVR

On Sun, Mar 28, 2004 at 12:38:03AM -0800, LightYearCS wrote:

> So, really SPI is it right? :)

Yep.  Like Larry said, though, be careful setting fuse bits.  By
default, the chips come set to run with the internal oscillator at 1
MHz.  You'll normally reprogram the fuses to run at a higher
frequency, and/or to use an external crystal.  There are fuse
settings, however, to run with an external clock signal, in which
case, unless you have an external clock attached you will lose the
ability to reprogram the chip after you make that change.  You can
recover by feeding in the external clock that the chip is expecting in
that configuration, reenter programming mode, then reset the fuse bits
as needed.

Just a little something to be aware of - this is probably one of the
more common problems when you had programming communication
established at one point, but for "some reason" it doesn't work now.

Also, for ISP programming purposes, which uses an SPI protocol, the
ATmega64 DOES NOT use the MISO/MOSI pins as labeled on the chip
pinout.  Look for PDO and PDI instead.  It does use the SPI SCK pin
for clock, though.  Be sure you double check your programming header
is connected to PDO and PDI instead of MISO and MOSI before ordering
your boards :-) See the "memory programming" section of the datasheet
to double check the pin mapping for ISP programming.

-Brian
-- 
Brian Dean
http://www.bdmicro.com/


 
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