Talk:Asynchronous serial communication

Stray paragraph

Why was this put in?

To limit cable costs, all telecommunication equipment employs multiplexing. For example Morse code employs a series of dots and dashes to represent a character. Dots are short pulses of electrical current compared to the longer dash pulses. Thus, short and long pulses are multiplexed on the same wire (circuit) over time. In modern telecommunications, pulses are usually the same duration and a group of pulses are sent together to represent one character code. A pulse can only be in one of two states but there are many names for the two states.

When on, circuit closed, low voltage, current flowing, or a logical zero, the pulse is said to be in the "space" condition.

When off, circuit open, high voltage, current stopped, or a logical one, the pulse is said to be in the "mark" condition. A character code begins with the data communication circuit in the space condition. If the mark condition appears, a logical one is recorded otherwise a logical zero.

This is a general discussion of electrical signalling and not really the point of this article. --Wtshymanski 17:45, 24 August 2007 (UTC)[reply]

Error in the diagram description?

Under the example communication diagram there is description:

"In the diagram, a start bit is sent, followed by seven data bits, a parity bit and one "stop bit", for a 10-bit character frame."

However, it seems to be more like 8 bit data and no parity bit (or for some reason parity bit is included - incorrectly? - in the data bits group and not described as such).

I do not feel sure enough to make the change, so I leave a note here for someone educated in the subject. —Preceding unsigned comment added by 88.199.35.124 (talk) 23:16, 25 February 2010 (UTC)[reply]

The diagram did seem to be inconsistent with the text there, so I changed the text accordingly. Parity is optional, and even, odd, and no parity were all used. --John Nagle (talk) 05:03, 29 May 2011 (UTC).[reply]

Patent 1199011, wrong citation?

Reading patent 1199011, cited in the text as the origin of the asynch system, I am not convinced that it is a start-bit, stop-bit based code. Page 1 line 60 says:

Instead of conecting the main conductors to the branch conductors through a sunflower (I take this to be a distributor) ... a series of positively acting transfer switch mechanisms are provided which act at the pauses between the successive impulses.

Given that the whole thing is written in terms of a polar circuit, with 1 represented by a positive line voltage and 0 represented by a negative voltage, this wording suggests that a brief zero line voltage was sensed between each successive bit to count to the next bit. That is, the data transmission format is inherently terenary, not binary, although the 5-bit code transmitted is a binary code.

I don't deny that Charles and Howard Krum invented the asynch data format. Their later patents, notably U.S. patent 1,360,231 clearly uses start and stop bits (and sunflowers, clearly shown in the drawings as distributors). Someone with the time to read these patents closely needs to work out the history more clearly. Douglas W. Jones (talk) 20:01, 6 January 2017 (UTC)[reply]

Pete Lancashire pointed me at a delightful article:

H. L. Krum, The Morkrum Telegraph Printer, The Armor Engineer, Vol. VII, No. IV (May, 1915); pages 308-314.

This article describes the use of a start bit, but does not describe the need for a stop bit. A rheostat on the receiver is used to get the motor speed close enough to synchronous. I think this is the right source to cite for the historical discussion of early semi-asynchronous systems.Douglas W. Jones (talk) 13:36, 6 September 2017 (UTC)[reply]

External links modified

Hello fellow Wikipedians,

I have just modified one external link on Asynchronous serial communication. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

Added archive https://web.archive.org/web/20090320151231/http://www.bitsavers.org/pdf/teletype/144_Model15_Descr_Feb31.pdf to http://www.bitsavers.org/pdf/teletype/144_Model15_Descr_Feb31.pdf

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 03:42, 11 July 2017 (UTC)[reply]

Incorrectly referred to as Baud

The "Operation" section of the article says that "The speed or bits per second of the line (often [is] incorrectly referred to as the Baud rate)."

Is it incorrect? That depends on what "correct" means. In the nomenclature of information theory, "baud" has come to mean the number of symbols transmitted per second. But in async-serial communication, as defined by this article, only two symbols are ever used; mark and space. Technically speaking, "Baud rate" and "bit rate" are two different concepts, but in the special case of async serial communication the numeric value of the baud rate and the bit rate will always be the same. 173.75.33.51 (talk) 02:01, 24 July 2019 (UTC)[reply]