Talk:RS-232

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Removed pending confirmation:

(Note that bits-per-second is not generally the same as baud; when techniques like Quadrature Amplitude Modulation are employed, more than one bit can be transmitted per baud. In most RS-232 applications, only very low bitrates have one bit per baud.)

Forgive me if I'm wrong, but isn't this person getting analogue modem signals confused with digital serial signals? -- Tim Starling 07:29, 25 Aug 2003 (UTC)

Sampling rates at the central office for voice lines prevent the baud rate from surpassing about 4 k baud; but the bit rate is higher because discrete signals represent multiple bits. But yes, this seems to go in another article.Waveguy 22:57, 25 Aug 2003 (UTC)

The quote above is correct, but probably doesn't belong here, because of what Tim said. It's really more relevant to the modem than to RS-232, although the two were almost synonymous in home computing (for the average user, at least), especially back when most modems were external. --radiojon 08:12, 2003 Sep 5 (UTC)

Contents

[edit] Serial Communications

The discussion of Serial communications would be better in that article (which also needs work). --Wtshymanski 21:34, 10 Apr 2005 (UTC)

Started tuning up the RS 232 article. Please leave the commented text till I have a chance to move it to serial communications.

You know, RS 232 doesn't really define a "bus" as I understand the term - it's more of a point-to-point connection, which is indeed one of the limiations I refer to in my contributions. --Wtshymanski 04:21, 11 Apr 2005 (UTC)

[edit] Name change from RS-232 to EIA-232

I wonder whether anybody would disagree if i change this article's name to EIA-232. Currently, a search for EIA-232 is re-directed to RS-232. IMHO, i think it should be the other way around. ie RS-232 should be re-directed to EIA-232. To support my opinion, below is a foot note from "Unix System Administration Handbook" 3rd edition page 94.

To be technically correct, RS-232 should be refered to as EIA-232. However, no one will have the slightest idea what you are talking about.

Please, say something as i plan to change the name sometime in future if this post doesn't generate objections.

OK, I object. The footnote you quote is true: Although EIA-232 is technically correct, nobody ever calls it that. Google gives 1,600,000 hits for RS-232, and only 57,100 for EIA-232; it's obvious the new name was never really accepted. And there are a lot of present (and probably future) articles that link to RS-232 that would need to be changed; not worth the effort. --Rick Sidwell 20:08, 3 May 2005 (UTC)
Object - RS-232 port is the more frequently used terms, though I've also seen it designated "EIA RS-232". Since this is what the standard was known as during it's heydey, I don't think a name change improves the utility of the article. A redirect from "EIA 232" to this article would work. --Wtshymanski 00:15, 4 May 2005 (UTC)
Thanks for feedback. I have to give in as i agree that changing the name will have too much ripple effect on other articles. gathima 00:33, 11 May 2005 (UTC)
It's not any more correct than RS 232. The current standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange (ANSI/TIA-232-F-1997 (R2002) (see [1]- so changing the article title to an intermediate, also obsolete, description seems bootless. TOo bad they don't say "Recommended Standard" but when you think about it, what other kind could there be? I would expect that most of the serial ports out there are labelled "RS 232" since revision C was the mostly widely referenced, though often ignored, edition of the standard during the Great Computer Boom of the latter 20th century. --Wtshymanski 14:05, 19 May 2005 (UTC)
  • That's what I thought. Thanks. SchmuckyTheCat 17:42, 19 May 2005 (UTC)


[edit] Why?

Why is the {{ipstack}} template here? It doesn't clarify the article any and most uses of RS 232 have nothing to do with Internet protocols. Would anyone object if I made it go away? --Wtshymanski 03:51, 24 May 2005 (UTC)

I agree; most uses of RS-232 have nothing to do with IP. The template keeps getting added back, probably because RS-232 was included in it... --Rick Sidwell 19:45, 5 November 2005 (UTC)
i've seen a similar thing happening over at ppp (i personally think that one is on the oppoisite side of the line to this one but you see similar slow addition and removals there too). The problem is the case of protocols that can be used as part of a tcp/ip setup but can also be used outside of it. Plugwash 21:09, 5 November 2005 (UTC)

[edit] What type is an RS-232

Is an RS-232 a Duplex a Half-Duplex or a Simplex, and why. I'm at a loss here.

Since both the transmit signal and recieve signal can operate at the same time, you could say the interface as a whole is full-duplex; each circuit, though, only ever operates in one direction and so is simplex. --Wtshymanski 14:16, 31 October 2005 (UTC)

[edit] framing of bytes in the stream?

If RS-232 doesn't specify this does some other standard do it or are there just some common conventions? it sounds like it would be pretty important for interoperablity. Plugwash 12:34, 4 November 2005 (UTC)

There are several different line codes that frame bytes in the stream in a variety of different ways -- for example, HDLC. But they are in the tiny minority of RS-232 interfaces.

The vast majority of RS-232 interfaces use ASCII with "start" and "stop" bits around each character. The universal asynchronous receiver transmitter mentions this is "by convention", but doesn't give a name to that convention. The start-stop transmission article seems to imply it is part of the ASCII standard, although the ASCII article doesn't mention it. What is the name of this line code / convention? Who standardized it?

I don't know who standardized it, but I can tell you that it dates back to five-level teletype machines... at least! It is not part of the ASCII standard; ASCII has to do with what the eight data bits mean, not how the bits are framed. Jeh 14:50, 30 June 2006 (UTC)

[edit] Style

If something is interpreted "idiosyncratically", it's also "selectively" though not necessarily the reverse - I think the phrase is redundant. Similarly, "DTE Equipment" expanded as "Data Terminal Equipment Equipment" would be clearly redundant...so I think "DTE Unit|Device" is also redunant. --Wtshymanski 23:07, 22 January 2006 (UTC)

[edit] RS-232 connector wire colors

I had to find which pin on a DB-9 corresponded to which color wire insulation, and I was unable to find that info online. SO, with a pin tester, this is what I got. I'm not sure how standardized it is, but this is a radio shack DB-9 mate to female cable. So, here's teh info, please fit it in somewhere appropriate if it's relevant:

pin1 - yellow
pin2 - orange
pin3 - red
pin4 - brown
pin5 - black
pin6 - teal
pin7 - blue
pin8 - purple
pin9 - gray

67.83.198.59 01:52, 22 March 2006 (UTC)

I strongly suspect its manufacturer specific and you'd be pretty mad to assume it was true without checking. Its not like USB where a special cable type is used (in a usb cable the data pair are twisted and the power pair are somewhat larger than the data pair). Plugwash 10:39, 22 March 2006 (UTC)
I can confirm that. It doesn't match on mine (generic DB-9 male to female cut in half). 81.107.46.167 07:58, 29 July 2006 (UTC)

[edit] EIA

Can someone check to see if EIA represents: Electronic Industries Alliance or Electronic Industries Association? They are similar, and easily confounded.

It's the Electronic Industries Alliance. Confirmed by their web site, including how it is designated in their bylaws. --Brouhaha 16:40, 31 May 2006 (UTC)

[edit] What are the Associated OSI Model Layer(s)?

--143.92.1.33 10:01, 1 August 2006 (UTC)

I've never found the OSI model to be particularly useful in understanding *any* communications system. Every single paper has that "apartment block" diagram and then that's the last you hear of the OSI model. I suppose RS 232 is physical layer - you can't get further down than defining what's a 1 and what's a 0, anyway. --Wtshymanski 17:30, 1 August 2006 (UTC)

[edit] focus

You know, there's a terrible tendancy especially in the electrotechnology articles on Wikipedia to put *everything* we know in one article. There's no need to cover everything pertaining to the topic in *every* article. That's what LINKS are for. Taken to the ultimate, we'd only need one article titled The sum total of human knowledge to date . --03:34, 13 August 2006 (UTC)

if we actually knew where theese conventions came from we could possiblly move them there, but splitting them out into a general conventions used with RS-232 article when this article is not hugely long anyway seems kinda pointless. Plugwash 12:56, 13 August 2006 (UTC)
But we've got a perfectly good article on computer serial ports which is the place to talk about stuff like bit rates - which is NOT in the standard and so doesn't belong in this article. Baud rates are already shown there. Incidentally, do the rates 115k and higher actually work, or are they some PC tweaker stunt with no application in the real world? I've never seen a store-bought RS 232 device that recommended baud rates higher than 38.4 k (which isn't strictly allowed anyway). I haven't done the maths yet but would a compliant port even have TIME to slew up to 12 volts at 400,000+ bits per second? --Wtshymanski 15:26, 13 August 2006 (UTC)
Hmm that link in your first paragraph is red and the search doesn't seem to be finding anything. Its fine by me if this article becomes about the standard alone so long as there are clear pointers to another article which actually discusses real "RS-232" ports. Plugwash 16:57, 13 August 2006 (UTC)
The link in the article's first paragraph is correct, though, and I've fixed my red link above. Serial port is the place to talk about one set of baud rates. ==Wtshymanski 23:45, 13 August 2006 (UTC).

[edit] pins and signals confusion

I find it somewhat confusing that a DCE receives data on the TxD pin and transmits on the RxD pin. My edits that attempted to clarify this were reverted. The situation is made more confusing by the fact that some vendors mislabel their DCE ports to try to make them seem more sensible. Another source of confusion is that some signals/pins have no counterpart. TxD and RxD are roughly "opposites", as are DTR and DSR. DCD has no such counterpart, yet it is used in some null-modem cables! Can someone suggest a better way to clarify these issues? -- Austin Murphy 19:30, 16 November 2006 (UTC)

I think the sentence "The signals are labeled from the standpoint of the DTE device" makes it pretty clear. I personally don't find it confusing that some DCE signals don't have DTE counterparts. Think of the DCE as a modem; these "extra" signals are things you would expect, like "incoming call" (RI) and "connection with the remote modem established" (DCD). The latter is especially important; when it isn't asserted, the DTE thinks it is communicating only with the modem (e.g., for call setup), not the DTE at the far end. Not all software cares, but a general null modem needs to assume it does and somehow assert DTE when the remote device is connected (typically by connecting DCD on one side to DTR on the other).
Maybe a diagram showing both the local and remote DTE's that want to communicate with each other along with the two DCE's they are directly connected to using the RS-232 interface would add some helpful context. (It would be useful for the Null modem article as well.) After all, although the purpose of RS-232 is only to connect a DTE to a DCE, this is only part of the overall goal to allow the DTE to communicate with another DTE. Most often today, RS-232 is used to to directly connect two devices, so this subtlety is easily overlooked. --Rick Sidwell 01:24, 9 January 2007 (UTC)

[edit] RS232 as voltage source

How much current does the standard allow you to draw from a serial port? It's not unusual to "steal" voltage from it to supply small gadget and devices. TERdON 14:55, 6 January 2007 (UTC)

  • The standard says (at least in Rev. C) that the terminator shall have an impedance between 3000 and 7000 ohms, and not more than 2500 pf of capacitance. But that's while maintaining all the other requirements for communication. The standard (up to Rev. C) doesn't say anything about powering devices from the interface. So, the answer is "Try it and find out" - from bitter experience not all serial ports have enough jam to drive all so-called "port powered" devices, which is why I don't buy them any more. --Wtshymanski 03:06, 14 January 2007 (UTC)
    • Afaict no power thief can ever be compliant, simply think of the case of connecting two power thieves to each other. A power thief always requires the port it is connected to to have more drive than it can provide to the signals back. Plugwash 15:34, 16 January 2007 (UTC)

[edit] Reference wanted

The standard (at least Rev. C) says the maximum slew rate is 30 volts per microsecond. If you are using +15 and -15 volt levels, sounds like 1,000,000 bits/second could be achievable...certainly more than 20,000 bits/second. Can anyone produce a citation saying that going faster than 20,000 bits per second exceeds the standard's limit on slew rate? I'm taking this out till I see a reference. --Wtshymanski 03:06, 14 January 2007 (UTC)


[edit] PCI-E RS232 card

[2] lol —The preceding unsigned comment was added by Towel401 (talk • contribs) 00:38, 3 February 2007 (UTC).

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