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'[PIC]: best MCLR setup for ICSP'
2001\02\05@124951 by Mike Mansheim

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[forgot the tag - sorry for multiple posts]

What is the best way to wire MCLR for ICSP?
(referring to the permanent interface between pin 1 and the rest of the
circuit, not the temporary interface to MCLR during ICSP)

The ICSP guide is unclear on this, in my opinion.  It says that there is
typically an RC on MCLR, and recommends a diode in that case.  We don't
need the RC (because we use the power up timer), so we've always had
just a diode between MCLR and the 5V supply.  However, I have *finally*
figured out that, for programming to work properly, the chip needs to
be reset by pulling MCLR low, then put into programming mode by raising
MCLR to Vpp (this is undoubtedly painfully obvious to most of you - my
apologies).
With our diode only setup, anything that tries to pull MCLR low will short
its own 5V supply, which explains some odd voltages I've seen when
watching on a scope a promate ICSP one of our existing boards.
Is a resistor in series with the diode the best approach, or a resistor,
or something else?
Why does the ICSP recommend a schottky diode?
I'm now amazed the promates managed to get the job done for a couple of
years with our existing design.  Any thoughts on why?
Other than being able to program properly, is there any way of quickly
checking that the chip has actually entered programming mode?

Thanks for any help.

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2001\02\05@202502 by Roman Black

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Mike Mansheim wrote:
>
> [forgot the tag - sorry for multiple posts]
>
> What is the best way to wire MCLR for ICSP?
> (referring to the permanent interface between pin 1 and the rest of the
> circuit, not the temporary interface to MCLR during ICSP)


Hi Mike, in my apps I use a 68k resistor from MCLR
to +5v. Simple and cheap, never had a problem. I
suppose it depends how bad you need brown-out circuits,
etc.
-Roman

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