Dear Friends,

I am using matrix keypads in 3X4 and 4X4 configuarations in most of my products. I have always used following configurations when i used them with P89C668, P89C669, P89V51RD2 & P89LPC922.

- Columns connect to 4 port pins and port pins are configured to read.
- Rows connected to another 3/4 port pins and these are configured as outputs.
- 1k Pullups connected to port pins of micro where columns [ read ] is connected.

I used these pullup to provide enough current when a contact is read so as to avoid dry contact problem. Also these pullups dont let the input side [ columns ] float when no key is pressed.

Now I came across this philips appnote,
http://www.standardics.philips.com/support/d...n10184.pdf

In this appnote they show reading of keypad without any pullups on read side pins [ columns ]. Is this method going to work, how?

In this method there is not enough current to avoid dry contact is there? and inputs may float too?

Thanks & Regards,
Prahlad Purohit