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'[EE]: PIC 16f877 Programmer'
2001\02\06@014337 by Jeethu Rao

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Hi Guys,

I am designing/constructing a programmer for PIC16F877 and PIC16F84. Now, to reset a PIC from Programming mode, is it enough if I can bring the voltage on MCLR to 1.35 volts ? or should it be 0 ?

I.e What is the maximum permissible voltage on MCLR to achieve a Device reset?

Jeethu Rao
http://www.jeethurao.com

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2001\02\06@073633 by Bob Ammerman

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Hi Guys,

I am designing/constructing a programmer for PIC16F877 and PIC16F84. Now, to
reset a PIC from Programming mode, is it enough if I can bring the voltage
on MCLR to 1.35 volts ? or should it be 0 ?

I.e What is the maximum permissible voltage on MCLR to achieve a Device
reset?

Jeethu Rao
http://www.jeethurao.com


The 16F84 data sheet says "0.2Vdd". This is 1 volt on a 5 volt supply.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\02\06@131745 by Barry King

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You asked:

> I.e What is the maximum permissible voltage on MCLR to achieve a Device
> reset?

On the 16c76, which is the datasheet I have in front of me, "V in
low" for -MCLR is 0.2 Vdd, for a 5 V supply, that's 1 V.  Check some
others, they may vary.

Lower is better, because you have more noise margin.  Also, lower
impedance is better becuase you can ensure a fast enough transition
on MCLR.  Driving MCLR for programming is especially critical because
you have to be careful about the part starting to run while MCLR is
slewing, and therefore having a non-zero PC when you start
programming.

Sounds like you have a marginal drive circuit if it might not go
below 1.35V.  IMHO you should buffer it somehow to ensure that it
will drive MCLR rapidly to the voltage you want.

-Barry.
------------
Barry King
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Check out the accumulated (PIC) wisdom of the ages at:
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2001\02\06@171202 by Tony Nixon

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Jeethu Rao wrote:
>
> Hi Guys,
>
> I am designing/constructing a programmer for PIC16F877 and PIC16F84. Now, to reset a PIC from Programming mode, is it enough if I can bring the voltage on MCLR to 1.35 volts ? or should it be 0 ?
>
> I.e What is the maximum permissible voltage on MCLR to achieve a Device reset?
>
> Jeethu Rao
> http://www.jeethurao.com

I would take it as low as possible.

The devices can stay powered up through an IO pin, even marginally, not
sure about MCLR.

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Best regards

Tony

mICro's
http://www.picnpoke.com
spam_OUTsalesTakeThisOuTspampicnpoke.com

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