Hi,

Amost all the requirement has been explained by Jacek two messages up here.

However,whatever approach you adopt, all pins to ground (in case very small number of keys) OR a matrix, row/columns (in case of say 100 keys 20 by 5 keypad), you have to decide whether you need an interrupt to tell the micro if a key is pressed while busy doing other things or you can afford all the times scanning the ports to keep watching when a key shall be pressed waiting.

You can OR either rows or columns whichever is less in number and connected to ground. Out of the OR can go to an external interrupt.

Just to say. There can be a hundred ways to do keyboard things.

Simon


PS:

If you want there are application notes along with the C code to connect the standard PC keyboard to 8051. Only two pins are used, funny isn't it.