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how to make switching keypad

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pritee

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m having 4*4 matrix keypad.how can i scan only 4th row & 4th column? i want to make keypad like my 16th key is common when that key is on then keypad should generate alphabates on uart for 4*4 matrix keypad and when key is off it should generate numeric characters.pls help me
 

A solution:

Use this 16th key as a toggle switch (like the caps-lock on the PC keyboard) and store this state in a bit-variable,
which will change the look-up tables (numeric <> alpha).
An additional LED also can be lit to visualise the keyboard state (like on the PC keyboard :))

Thus, you can use the usual routines for the 4x4 keypad (no additional HW).
 
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    pritee

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i unable to write program for toggle key?? :-(
on same matrix i checking status of toggel key and look up table
 

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