[time-nuts] Clocking a PIC16F628A from a Rubidium Standard

Don Latham djl at montana.com
Sat Nov 26 17:36:46 UTC 2011


Come on, folks. never hook anything directly to the power line. The
source is just too stiff. Use an opto. I used fiber optic isolation with
my big DC power supply.
Don

Orin Eman
> On Fri, Nov 25, 2011 at 1:21 PM, Robert Atkinson
> <robert8rpi at yahoo.co.uk>wrote:
>
>>
>>
>> Hi,
>>
>> Microchip cerainly condone using input protection diodes of PIC
>> devices as
>> clamps. There are application notes for zero-crossing detection which
>> connect the input to the 115V AC line via a resistor. Note that these
>> are
>> intentional protection diodes, not unavoidable parasitic junctions.
>> Typical
>> Absolute max clamp current (inc. 16F628) is +-20mA.
>
>
>
> Yes, absolute max - that below which the part doesn't let the magic
> smoke
> out...  but note the comment below the absolute max ratings (I'm taking
> this from a PIC16F88 datasheet since I happen to be using this part):
> "This is a stress rating only and functional operation of the device at
> those or any other conditions above those indicated in the operation
> listings of this specification is not implied. Exposure to maximum
> rating
> conditions for extended periods may affect device reliability."
>
> Note also the max voltage on any pin is something like Vdd+0.3V.  One
> wonders how much conducting their diodes do with 0.3V across them.
>
> Personally, I don't let the protection diodes conduct in normal
> operation.
>
> Orin.
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-- 
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com





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