At 03:59 PM 3/31/2005 -0300, Mauricio Jancic wrote:
>Well, in this case it does. The pic is powered by a 4 1.2V battery pack, so
>voltage range will be between 6 V and 2.5 (aprox). The PIC is actually
>working but the customer is asking for a complete verification on the entire
>VDD range... Would it be possible to fail this test? Why? Once the PIC is
>programmed, if it is designed to work on a given Vdd range why would it fail
>to verify??!

Flash cells can be "marginally" programmed and flip over
if operated at a voltage that is different from what used to program the Flash.
This however only happens in practice if during production of the chips the
process runs outside of its specified parameters (i.e the manufacturer' 
process controls
are not good/sufficient) of if the device datasheet specs do not leave 
enough safety margin
for slight process variations (i.e the manufacturer is pushing the 
datasheet spec to the limit of
what the process is actually capable off.)

Interestingly enough this "flip" over effect can happen ANYWHERE in the Vcc 
operating
band (let's say at 3.76V, but not a 5V, not at 2V and not at 3.7 V) , so 
just verifying at Vccmin and Vccmax
does not guarantee you anything.
If you wanted to be 100% sure you had to sweep the entire Vcc range
over which your application operates and verify the Flash contents.

best regards
Volker
MicroController Pros Corporation
The MicroController and Embedded Systems Tool Store
http://microcontrollershop.com
+1-408-333-9266 Phone
+1-800-510-3609 Toll-free phone
+1-215-243-6071 Fax 
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