> Thirdly, as far as applying higher than supply voltages to inputs of 
> a PIC, there are
> PICs and there are PICs. The amount of current you inject, and what 
> polarity it is, will
> affect operation at different levels depending which PIC you choose. 
> The 16C54
> allows 500uA without affecting operation. As new PICs have been 
> introduced, that
> value has decreased but is still nonzero, especially if you are not 
> using analog
> features in the PIC.

Alas, the above statement re the 16C54 is incorrect.

What the data sheet does say is that:

1.    Absolute maximum ratings are:

- Maximum clamp current into any pin out of the pins included in the 
set [T0CK1] = 500 uA max.

- Maximum clamp current (for the IC presumably as it does not specify 
by pin) = 20 mA.

There is NO guarantee of not affecting operation at these levels - it 
just guarantees that the chop won't die.

2.    Operating voltages for all input pins are

- A minimum of Vss.

- A maximum of Vdd.

The above data is not stated directly but needs to be inferred by a 
careful reading of the operating section of the data.

Nowhere in the operating section does it mention taking any I/O pin 
outside the Vss-Vdd range. [[I'll say "nowhere" to encourage people to 
prove me wrong. I didn't see it in a reasonably careful but not 
painstaking look, and I'm not surprised.

Nowhere does it state an acceptable current in the protection diodes 
when operating.

I hammer this pont again and again and again and ... over the years 
because

- I have a bee in my bonnet :-)

- It's very important and most newcomers try to expand what the data 
sheets say to areas where they don't apply. It's good to learn early 
on what a data sheet does and doesn't say and the danger of 
transferring statements from one section of a datasheet to another.

Flame shields u....<too late> :-)



        RM


Make my day.
Find areas where I'm wrong - they're sure to exist, even if the 
general principle of what I'm saying is correct (as it is). By all 
means pore over the datasheets and decide for yourself if they say 
what I say they do.


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