i can't imagine an application that requires 1600 buttons

me too, thats why I asked him whether he is sure about what he has posted.

Jose said:

First expand your I/O to 80 lines!!

Prahlad replied:

Not necessary to have so many I/O. Not even for a 40X40 Keypad. I can do this with 8+10=18 lines.

Prahlad, just think what you have achieved with 5 buffers and five latches? You got 80 I/Os. Thats what Jose mentioned.

BTW: Your scheme seems wrong. Why use 74HC573 on both columns and rows? On one side, there should be buffers, not latches.