Mr. William Chops Westfield gives a very clear and well written explanation below. >From posts you (kenasw) have made since then I see there are still some things that you have questions about. There is no UART standard. The U in UART stands for Universal (fits all requirements). The UART was originally a chip that was used to connect a Data Terminal Equipment (DTE) or computer, to a Data Communications Equipment (DCE) or modem, using the RS232 Protocol. The modem was usually hooked to a phone line. Here are some good details. RS232, cables and UART's http://www.lammertbies.nl/sitemap.html RS232 http://yarchive.net/comp/rs232.html I will take a big chance and say that RS232 was not designed to connect computer to computer. So when connecting equipment using what each equipment maker calls RS232 is not always plug and play. Some will need some wires crossed and or signals jumpired. A null modem cable takes care of most of these problems along with a couple of gender changer plugs. The UART is one of the mile stones in computer development. It was the first I/O chip for a microprocessor that had it's own intelligence. The computer software set it up and pumped data, the UART would send the byte, and interrupt the computer when it was ready for another byte. It also checked for certain error conditions. The UART being universal, was capable of RS422 and RS485 protocol. These standards are used for better noise immunity over longer distances than RS232. It could also use the 5 bit baudot code. What you do with the signals in and out of the UART depends on what they go to and how far it goes to get to where it hopes to go to. Baud rates are up to you also. The baud rate for the MIDI musical devices are a odd one until you realize that they are derived from the 1 mHz cpu clock from olden times and therefore did not require a separate crystal for the UART. So all you need to do is to match what you are communicating with and if you "roll your own", be concerned with noise the father you go. Bill ----- Original Message ----- From: "William Chops Westfield" To: "Microcontroller discussion list - Public." Sent: Friday, May 13, 2005 8:48 AM Subject: Re: [PIC] RS232, USART, and COM > >> What would be the difference between rs232, usart, and pc com port. > > COM is a logical device name, more or less specific to windows/dos. > (it would be /dev/tty under most unix systems, for instance.) > > Normally, COMn connects to to a particular type of asynchronous serial > communications port. "async serial communications" implies a standard > for bit ordering, timing, synchronization, and error conditions that > allow for sending computer data over a single wire (in each direction.) > (X.20 describes it, I think, although a uart manual probably does > better.) > A UART is the common name for the device that interfaces to a computer > on > one side and the serial port on the other. However, a uart is digital > logic device, so the serial output is still at digital logic levels. > > To move serial data across significant distances, digital logic levels > are not ideal, so there are additional standards that describe how to > shift those levels for more reliable long-distance use. rs232 is one > of these standards. It's a rather complete standard defining how two > devices talk to each other with serial ports. It is the most widely > violated standard in the world, and includes lots of bits and functions > that no one uses any more (it specifies a 25 pin connector, and has a > use for nearly all of the 25 pins.) When most people say rs232, they're > talking about the most basic pieces - the voltage levels representing > a zero or one on each signal line. These voltages are "inconvenient" > for > digital logic to produce, and so there's usually a separate chip to > do the conversion. > > The three are completely orthogonal; you can have com ports that are > are actually network connections, serial ports that aren't "async", > serial ports that aren't rs232, and rs232 ports that aren't async > serial. > > BillW > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist