heloo
what are differences between SPI, UART and USART.
do our present arduino works on all three platform.
WHat are differences between these three serial communication.
A UART is a Universal asynchronous receiver/transmitter. The most well-known implementation is for serial ports on PCs, where the 16550 is (or was, anyway) ubiquitous. It is an IC. A USART is similar, except that it also provides synchronous serial capability. Whether you could get one to work with an Arduino would depend, I guess, on the which chip you were trying to use, and how much work you wanted to put into programming. Since the Arduino already has TX/RX pins, and there are many existing solutions for serial communication, I don't think I'd be looking around generically for UARTS. I admit that I don't know, for example, whether the Maxim 3322E fits the definition of a UART (I suspect it does), but there's already information on using it. Or search the forum for RS485. I'm sure there are many options for serial communications, but it depends a lot on what you're trying to do.
SPI is SoyuzPlodImport, a Russian company known for being the producer of Stolichnaya vodka. I prefer Ketel One myself, but Stoli is pretty good stuff too.
Or, it could be the Serial Peripheral Interface Bus, which defines an electrical and communications standard for serial communication among devices. There is a SPI library for Arduino.
There's a handy search box at the top of every page. It will find lots and lots of info for you. 
Do I get to say Neener-Neener now? ]
i use arduino 2009
which of this serial communication features does it supports.