IMHO there isn't much common in terms like RS485, packets and optocouplers.... You can't use packets with RS485 because there is a different way how to share a bus. You can't use optocouplers because there is no way how to feed 485 transmitters from a bus. Igor -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Oliver Broad Sent: Monday, April 21, 2003 7:36 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [PIC]: USART -> RS232, Transceiver Chip Required? OK so I'll say "Asynchronous over RS485" instead. The fact that there is no data packet specified was part of the problem I suppose, giving manufacturers free reign to do as they please. I'm starting to like the idea of transformer coupled alternate pulse inversion interfaces like the one used for ArcNET sometimes. The low cost of 485 is lost if you add optocouplers and a DC-DC converter for an isolated interface. Longer pulses could require a transformer with a larger Et product. I figure that using IRDA UARTS or adapter chips would be the easiest approach to seperating bits, to ensure that adjacent bits were sent with alternate polarity. ----- Original Message ----- From: "Douglas Wood" To: Sent: 21 April 2003 05:25 Subject: Re: [PIC]: USART -> RS232, Transceiver Chip Required? > You do realize that "RS485" is an electrical spec and has no protocol or > data packet component to it at all. > > Douglas Wood > Software Engineer > dbwood@kc.rr.com > ICQ#: 143841506 > > Home of the EPICIS Development System for the PIC > http://epicis.piclist.com > > ----- Original Message ----- > From: "Oliver Broad" > To: > Sent: Sunday, April 20, 2003 2:36 PM > Subject: Re: [PIC]: USART -> RS232, Transceiver Chip Required? > > > > 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 > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu