Hi Vignesh,

I just read through the thread and did not find any reference to debouncing the keys ( or if I missed it I am sorry ).

When you are handling key presses without debounce, code like this will produce completely unpredictable results :

while(P0^7==1);
     TR1=1;
     while(P0^7==0);
     TR1=0;

Due to contact bounce, both conditions will be satisfied in rapid succession and even though your code would have been executed, it is of no use to you. The bouncing contact would have simulated many press and release conditions.

Some suggestions to overcome this :

> Instead of querying key presses directly, query the stored image of the key presses. You can run a basic 5ms interrupt based timer and within that ISR update the input key status - and establish a routine to AND the previous image with the current image. The main will then read only the result of this ANDing when it requires to check status of any pin. You will have thus effectively debounced the key presses by 10ms. This is a generic guideline - the timings, methodology etc have to be worked out to suit your specific need.

> Use a hardware debounce chip. Check MAXIM site for options and application notes on this debounce issue.

Raghu