On Thu, 26 Mar 2009, Rick wrote:

> Looking for advice on a way to insure that only one of four push buttons is
> active at one time. (IE - prevent multiple button press's) I have 4 pushbuttons
> on Port A (16F88) and have AND'ed these bits out. The only idea that I've tossed
> around so far is to rotate the bits and count them.. If count = 1 then only one
> push button is selected. Is there a better way to do this?
> 
> Regards,
> 
> Rick

A very simple solution would be to have an array of 16 flags. Each flag 
corresponds to a combination of pressed switches. You would use each flag 
to tell you if the combination is valid or not.

0000	0	no buttons pressed - invalid
0001	1	only button 0 pressed	- valid
0010	1	only button 1 pressed	- valid
0011	0	buttons 0 and 1 pressed	- invalid
0100	1	only button 2 pressed - valid
0101	0	buttons 2 and 0 pressed	- invalid
0110	0	buttons 2 and 1 pressed	- invalid
0111	0	buttons 2, 1 and 0 pressed - invalid
1000	1	only button 3 pressed	 - valid
1001	0	buttons 4 and 0 pressed	- invalid
etc to 1111

then all you would need to do is use the pattern on the input port (masked 
so that it only looks as the pushbutton inputs) as an index into the array 
to see if it is valid or not.

Regards
Sergio Masci
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