I want to know difference between CLPD and CPLD
and I want to know the difference between a duck :-}

Well, humor aside, I assume you mean
I want to know difference between PSD and CPLD
The PSD chips were/are developed as a companion chip to the '51 and in the OTP version have been around for a long time. The PSD chip basically is a small PLD and some RAM. The original PSD chip from WSI (now bought by ST micro) when connected to a '51 provided 2k of ROM and 3 'ports'. These 'ports' were memory mapped I/O. Today the PDS chips are equipped with flash instead of OTP. for information go to href="http://us.st.com/stonline/index.shtml

In my opinion, if the PSD people, when they started, had brought out a preprogrammed version, the 8255 use in '51 designs would have been extinct, but, they only sold 'you program' OTP chips and all but the big users could not afford to develop on a "while you learn throw away a lot of chips" platform. Today when they have flash parts, the train has left the station, the RAM has moved inside the uC or more than the PSD provide is required and I/O flexibility is so much better with an unrestricted CPLD.

ST has introduced some '51 based PSD micros, some day I'll have a look - too busy to think of new platforms.

Erik