Wow, thanks for the summary, I didn't notice this thread until now. That is
an excellent design! 10keys with only 4 I/O ports used!?? Gonna file this
one in my "info" file... TTYL

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of James Newton, webhost
> Sent: April 12, 2003 18:03
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [OT:] different approach to keyboard scanning?
>
>
> source= http://www.piclist.com/postbot.asp?id=piclist\2003\04\11\174744a
>
> Let me see if I have all this right. Combining Scott and Eric's
> comments you
> could do this:
>
>     0   1   2   3  GND
>     |   |   |   |   |
> 0---+--KEY-KEY-KEY-KEY-
>     |   |   |   |   |
> 1---+---+--KEY-KEY-KEY-
>     |   |   |   |   |
> 2---+---+---+--KEY-KEY-
>     |   |   |   |   |
> 3---+---+---+---+--KEY-
>     |   |   |   |   |
>
> Weak pull-ups enabled, first read the port and check for any lows, this
> would be a key on the GND (far right) column. If all pins are high, ground
> pin 0 and any lows on 1 thru 3 would be a key in the top row.
> Then ground 1
> and a low on 2 or 3 indicates the two keys on the second row
> (other than the
> last column), finally ground 2 and check the remaining key (on the third
> row) by reading back 3.
>
> That is a 10 key pad in 4 IO lines with no external components other than
> the keys.
>
> ---
> James Newton: PICList.com webmaster, former Admin #3
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