>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 14 April 2005 13:30
>To: Microcontroller discussion list - Public.
>Subject: Re: [PIC] Matrix Keyboard Philosophy
>
>
>Harold Hallikainen wrote:
>
>>> Why don't you tri-state the output lines that you don't 
>read? No need 
>>> for extra parts, and no chance of connecting two outputs together.
>
>> Excellent idea! Just write to the TRIS instead of LAT! And, it takes 
>> no parts!
>
>Just don't forget that these "outputs" are now usually 
>floating inputs while tri-stated. So you should make sure that 
>they never stay long in that state. This usually is given, as 
>you usually poll quickly and cyclically through all drive lines. 
>
>The "proper" approach would be pull-ups on the output lines. 
>But that's extra parts, and equal in parts count to your 
>approach of series resistors in the output lines.

Or use PORTB with it's internal pullups.

Regards

Mike

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