On 2/23/06, kerri <kerri1111111@btinternet.com> wrote:
>
> I may then have a problem on my board, however I have this question:
> As you said RB4 and RB5 are defined as inputs, but are not trist_ed
> into this mode because they are using the fact that ALL pins are input
> anyway after reset, right? If so, it seems very strange that it is pin RB5
> which seems to be sensitive to no pullup and the other pins (all the
> other ports, about 32) are not having this problem. Try not pulling up
> RB5, leave it unconneted, see if you get this problem, then if you do,
> can you explain why RB5 is sensitive, rather than any other port pin
> of which there are many.
>
> Also, as you say yourself, microchip left all unused pins in input stage,
> so it seems this is not the same as per the advice some people here
> seem to be giving - to configure unused pins to output.
>
> If I am repeating myself I am sorry, I just want to make sure that
> I am being understood. Thanks.
>

To put unused pin to defined status is a good engineering practise.
To do that you can do the following two things:
1) to configure the unused pin as input and use pull-up/pull-down
resistor to put them into define status (high or low).

2) to config the unused pin as output and then output high or low to
put them into defined status (high or low).

If you do not do this, there is no guarantee that it would work or
would not work in certain situationns. In this case, RB5 causes problem
for you. In another case, maybe another pin causes you problems.
Worstly, it may not cause problems during testing stage but the
problems may pop up in the field.

Microchip's board is a demo board. It may or may not follow good
engineering practise but generally they serve their purpose well.
But there are some ugly application notes out there as well. In this
paticular case, it is a bootloader. It is the user's repsonsibility to
design the hardware/firmware to use the bootloader or modify it.


Regards,
Xiaofan

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