On Thu, 18 Aug 2005 10:49:22 +0200, you wrote:

>> As I said, it's a compromise. You have to decide the risks of 
>> failure and costs of recovery versus code usage.
>
>I seriously think in most cases a switch to a larger PIC would be a
>better choice than risking a field problem.

In cases where you are using it for field upgrades, and where field upgradability is a significant
design goal, I'd entirely agree.

However I'm  thinking more along the lines of situations where in-system upgradability is a 'useful
addition' but only if it can be done for little code cost, and in that context there are many
situations where it could be very appropriate.
e.g. in the factory - if it means you can upgrade without taking the product apart for the price of
a small amount of code, and if it occasionally fails the consequence is that you have to unscrew a
cover, then it is a definite benefit. 
Similarly in the 3v-supply situation - it allows in-circuit reprogramming of code-protected parts,
but if it fails, you fall back to cutting a link or whatever to apply 5V to reprogram.

However it should be remembered that if properly implemented, the risks of failure can be reduced to
pretty minimal levels.

You have to balance the extra cost you add to every unit by including a more robust upgrade method
against the cost of dealing with the probability  that (a) an upgrade is needed, and (b) that
upgrade failing and (c) the cost of dealing with a failed upgrade. In many cases (a)*(b)*(c)  will
be small that any extra initial cost is not justified. In others it won't, so you do it the more
traditional way. 



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