The code that Rob linked in his post is an option for you to consider. It offers a slightly different approach in that the multiple key pressed idea is ignored and replaced with the idea that each key in the matrix has a priority and the routine will report the key with the highest priority in the case of multiple keys pressed. The scanning algorithm uses a table lookup scheme so that this priority order can be determined at will just by re-ordering the rows in the table.

I have used this scheme many times, but it is not the ideal key scanning algorithm to use under several considerations....

1. If you have need for the concept of some keys operating as a "shift type" key. For example 'Hold down UP and press ENTER'.


2. If you need to use some key presses from the keypad in mutual manner. For example if you had a UP, DOWN, LEFT, RIGHT key set and wanted to support simultaneous UP and LEFT to slew an XY Table in both UP and LEFT at the same time as long as the buttons were pressed.


3. If there is a need to design an n-key rollover scheme on top of the low level scanning function the multiple key exclusion of the referenced code is a problem.

Good Luck
Michael Karas