I think there is a long standing practical joke by a previous generation of computer designers who intended to cause maximum confusion to those who would follow them. Take the TX and RX signals at the output of a typical UART... A 1 is 5v and a 0 is 0v ... OK Now this is inverted for RS232 so a 1 is MINUS 12v and the TX line idles in the 1 state so it idles at minus 12v Now handshake lines are introduced. These are asserted (true or 1) when POSITIVE. So in 5v form (unbuffered) they are negative logic so on a UART chip the lines may be designated inverted eg /RTS, /CTS etc But some chip manufacturers don't bother to label them that way. You'd be forgiven for thinking extra inverters were needed, though they aren't. Some IRDA implementations assume you will connect the LED and photodiode directly. Instead you would like to use a module with guaranteed specs...oh look the polarity needs inverting!!! RS485 is a bundle of laughs. You would expect that a device on a multidrop bus would simply ignore data not intended for it but some manufacturers products go further and sulk for a while just because a packet did not conform to their protocol. I tried to use a valve controller and some temperature controllers on the same bus, bunch of laughs that was. Eventually we got new roms. ----- Original Message ----- From: "Werner Soekoe" To: Sent: 14 April 2003 10:27 Subject: [PIC]: USART -> RS232, Transceiver Chip Required? Quick Question: If I use the USART of the PIC16F627 (or any other PIC with an USART) in async mode to communicate with a PC via a RS232 serial port, do I need to a transceiver chip such as the MAX232, or will it work without the transceiver? The datasheet I have on the PIC16F627 seems unclear about his, as do the application notes on the Microchip website. Thanks Werner -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body