Talk:EIA-485
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I'm requesting that this article have its history merged into EIA-485, where this article now is. (Someone else has improperly cut-and-pasted the article instead of moving it.) I made the request on the Helpdesk but got no response. –radiojon 02:00, 2005 Jan 31 (UTC)
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[edit] Confusion in A/B labelling
I have a problem with this article: The Waveform Example gets the polarity naming convention exactly wrong, and helps confuse people. Here is a good treatment of the confusing polarity issue: http://www.bb-europe.com/tech_articles/polarities_for_differential_pair_signals.asp -dgi, 12 June 2006
Can anyone provide a direct citation to the standard? I think the articles on the net like this one are just 50:50 stating that or the other. Petr Matas 23:53, 7 September 2006 (UTC)
EIA-485 spec, section 3.2:
"a) The A terminal of the generator shall be negative with respect to the B terminal for a binary 1 (MARK or OFF) state.
b) The A terminal of the generator shall be positive with respect to the B terminal for a binary 0 (SPACE or ON) state."
It's important to note that the MARK state is the rest state, i.e. the input to a transceiver from an inactive UART will be a logic high, i.e. a 1. I concur completely that the transceivers from the 75176A onwards are incorrectly marked. I am unable to find anything within the spec that supports the contention that the "A line can be designated by a '-' and the B by a '+'". (Steve Fairhead, sfdesign.co.uk) 195.112.48.103 18:31, 9 September 2006 (UTC)
[edit] connectors used with EIA-485
Is there a standard pinout for putting EIA-485 on a RJ11 or RJ45 connector? (Does 10BASE-T specify this, or are the signals on a 10BASE-T cable *not* EIA-485 signals?)
The article currently says "The following table lists some typical RS-485 signal pin assignments" then literally lists the pinouts. That is good information, but is there a name for these pinouts? Is there a name for the "EIA-485 on a DE-9 connector" standard?
I would like to fill in the holes in this table:
(table moved to Talk:Physical layer).
- The article says EIA-485 is just the signalling of bits, which means talking about the pinout of EIA-485, even typical pinouts of EIA-485, is nonsense. The author of the "connectors" section probably thought as I did until today that RS-485 referred to that RS-232-style character stream protocol. If not, I hope there is some other name for that protocol, and an article on that is where the connectors section and the pinouts belong.
Bryan Henderson 18:29, 13 September 2006 (UTC)
[edit] NMEA compatibility
The article currently states that NMEA signal naming is different from the RS483 standard (A- / B+). That is not correct. The NMEA standard says that " ... idle, marking, logical 1, OFF or stop bit states are defined by a negative voltage on line A with respect to line B" (in other words: A is the inverting signal); this is identical to EIA-485 as quoted above by Steve Fairhead. I also verified that NMEA V2.0, V3.0 and the corresponding IEC61162/1 are identical on this point. Heje/87.48.134.234 14:40, 17 October 2006 (UTC)
- I have updated the article accordingly. I also added some details about the EIA standard naming (and removed the mentioning of 5V - that is a arbitrary voltage and not a general value; I'm using 3V drivers myself and they give me 0.4V and 2.6V when terminated). Heje/87.48.134.234 15:31, 17 October 2006 (UTC)
[edit] External links
I removed the external links to Modbus sites since those links belong on the Modbus page. I also removed some commercial links to companies providing EIA-485 products since it was just general advertising for them unlike the TI and Maxim IC links which go to specific information about EIA-485 and not their own products. Littleman TAMU 20:33, 5 February 2007 (UTC)
I replaced on of the modbus links you removed with a RS-485 specific page from the same site, as it provides useful practical information to implement RS485. Please remove it if you see no fit for this link. 88.204.248.235 18:18, 1 March 2007 (UTC)
