Dear Erik,

Thanks for your reply, AFAIK there are four modes in LPC.
1. Quasi bidirection - std 8051 P1 P2 P3 type weak pull up can source hardly in uA.
2. Push Pull mode - can source and sink very well.
3. Read only - no source or sink only read.
4. Open drain - can sink no source like std 8051 port 0.

They put port 0 ie columns in quasi bidirectional mode & the rows P2.2 and P2.3 in push pull mode. They ground the rows and read the columns putting the rows low will let p2.3 and p2.2 sink the current and let the key get read in this mode the port 0 sources the current. But this current is in uA range wont this lead to dry contact? There are bugs in the code given in appnote too?

I dont think in this case LPC is doing any magic the rows as usual are quasi bidirection mode nothing new and columns too are used only for sinking ordinary AT89C51 type old micro can also do this. If this works then why at all we used pull up with keypads.

Thanks & Regards,
Prahlad Purohit