AVR-Chat

On Sun, Mar 28, 2004 at 03:05:46PM -0800, LightYearCS wrote:

> Now, do you usually need to remove the chip to reprogram?

Nope - not as long as you are using ISP (serial) method.  Many AVR's
can be programmed using a parallel method that generally requires
removing the chip from the board due to the higher voltages involved
(12V).

> So the fuses are "soft" fuses and can be reset huh?

Yep.  They set things like the type of clocking to be used (internal
oscillator, external crystal, external clock, etc), brown-out enable
and levels, startup delays, watchdog reset settings, JTAG enable, etc.

> Okay so basically the SPI interface (and yes, I knew about the
> alternate pins) is good to use, just make sure to NEVER blow the
> wrong fuse when programming.

Yes.  They do have a built-in failsafe such that you are not supposed
to be able to change the SPIEN fuse bit - the one that enables serial
programming, when programming using the serial interface.  But you can
still make it inconvenient by changing the clock settings to something
your board doesn't support.

> Normally I don't think I would even need to change the status of a
> fuse in the field.

Sounds reasonable.

Another method you might consider is to use the boot loader feature
where you can install a seperate program in FLASH that will get
control at reset time, and it can decide whether or not to reprogram
the "main appliction" FLASH area.  For example, you can have it check
the status of a few switches or something and if they are pressed,
then download a new program from some interface in order to reprogram
the main application.  If the switches aren't set, just jump to the
main application and skip reprogramming.  The programming interface
could simply be a serial port and your customers wouldn't need a
programmer, just a PC with a serial port.  And I don't think you can
change fuse bits from this method of programming so there would be
little worry that someone would mess up the fuse bits by accident.

Good luck!

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