Justin. The idea is sound but I would probably use rather higher values (10=
x
?) for both resistors.=20

-- Bob Ammerman
RAm Systems

=20

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Justin Richards
Sent: Monday, May 13, 2013 1:12 PM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC]: 16F887 using port A for both input and output

I should perhaps mention that I want to use the same 4 pins for both input
and output incase that was not clear.


On 14 May 2013 00:58, Justin Richards <justin.richards@gmail.com> wrote:

> Just wanted to run this past the wisdom of the list.
>
> Port Pins RA4 - RA7 on a 16F887 are successfully driving a standard 2=20
> x 16 LCD (via a shift register).
>
> Want to add 4 push buttons (ENTER, EXIT, UP,DOWN).
>
> Possible solution
>
> use weak pull downs approx 4.7K from port pin to ground.
>
> use 680ohm from port pin to N/O push button then  to +V.
>
> PIC should still be able to drive pins high or low as needed to=20
> control LCD even when switch is pressed.  Quick test seems to indicate
this is ok.
>
> Current when PIN driven low and switch is pressed, I =3D V/R =3D 5/680 ~ =
7=20
> mA (+ LCD and shift reg loading)
>
> Is this plausible.
>
> Cheers Justin
>
>
>
>
>
>
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