Djula Djarmati wrote 2012-01-07 03:25:
>
>
> On 07-Jan-12 03:00, Djula Djarmati wrote:
>> On 07-Jan-12 00:47, Jan-Erik Soderholm wrote:
>>>
>>>
>>> Adam Walley wrote 2012-01-06 12:12:
>>>> Ok. I ran some tests and confirmed that the MCLR pin was indeed resett=
ing
>>>> the code,
>>>
>>> How ?
>>> It does sound as if you do not have any MCRL pullup resistor !?
>>
>> Yes, there is clearly no pull up on his schematic which shouldn't be a
>> problem if he is using internal MCLR.
>>

Yes. My point was that setting "internal MCLR" could have other
side-effects when re-programming the chip. We (at least I) do not know
if he has a programmer capable of handling that ("Vpp-before-Vdd).
My general tip if one does not absolutely need the MCLR pin as
an extra input pin, is to simply leave it as an external MCLR pin.
One less thing to worry about.

>>>
>>> Note that Microship still recomends an external pullup. At least in
>>> the 16F690 datasheet.
>>>
>>
>> I can't find that in my 41262a.pdf datasheet, can you please say where
>> they recommend that?
>> I can only find where they advise against connecting external MCLR to
>> Vcc directly due to external MCLR being very sensitive to overvoltage.
>>
>> Djula
>
> I just realized what you mean, the problem in leaving MCLR input
> floating is that despite turning MCLRE off, high voltage spikes on
> floating MCLR could disrupt normal operation by i.e. inadvertently
> entering programing mode.

Yes, that whas what I was thinking about. So "internal MCLR" does not
generaly save componenets, it does give one extra input pin, if you
realy need that.

Jan-Erik.
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