Talk:Serial Programming/RS-232 Connections

This module is already a bit long, but here are some more things that might be worth covering. (Perhaps accompanied by splitting the chapter!)

• Duplex (full, half, simplex)
• Baud rate detection
• RJ-45 connectors
• Using a breakout box
• Note that RS-232 uses unbalanced circuits, so twisted pair cables aren't useful
  • Baluns can be used to balance the circuits for longer distance transmission
  • RS-422 is similar to RS-232, but has the advantage of balanced circuits

---

Note that RJ-45 connectors are not standardized in regard to RS-232 protocols. There are some devices that use them, and there are enough wires with a Cat-5 line that makes it at least in theory possible to do RS-232 over Cat-5 with RJ-45 connectors, but it is not commonly done that way. In fact, the only "standard connector" specified by RS-232 is the DB-25 connector.

Rob Horning 21:55, 25 May 2005 (UTC)

Discrepancies - Possible Errors

• According to the D-subminiature article, DE-9 is the correct name of the 9 pin D-shell connector. Links are now added for the D-shell connectors, but each instance of DB-9 should perhaps be replaced with DE-9 (possibly with a note about this common misnomer using a reference to Wikipedia:DB-9.)
• RS-232 signal levels are described more precisely in Wikipedia:RS-232#Voltage_levels than in this Serial_Programming:RS-232_Connections#Wiring_Pins_Explained. The signal levels are not always +15V and -15V. Consider replacing parts of this section with a reference to Wikipedia:RS-232.
• The claim that the handshake signals use negative voltage to indicate "Ready" contradicts my experience. The Wikipedia:RS-232#Voltage_levels descriptions about "negative voltage has the functional significance of OFF" and "positive has the function ON" also support my experience that e.g. Data Terminal Ready is positive when the DTE is ready and negative otherwise.

KV 02:00, 25 Jun 2005 (UTC)

Be bold in editing this if you see factual errors. The information I have put in comes from more technical books related to the subject rather than any "hands-on" experience of messing with the voltages directly on a circuit design level. I would like to see these changes, however, be based on something concrete and formal specs.

The +15V and -15V signals are a part of traditional RS-232 specifications, however. This admittedly is an older spec, and there are ranges of voltages to consider, with newer serial drivers going more toward the +/-5V range or less due to their use in embedded devices. Still, if you were trying to hook something up to a 30 year old industrial controller using RS-232 connectors, expect the 15V line voltage, or even higher.

My experience when trying to purchase electronic components, parts, and cables, the suppliers understand the term DB-9. Until you mentioned the possible term DE-9, I had honestly never even heard of it. I guess from a purest viewpoint it should be called a DE-9 connector, and the Wikipedia article explains it pretty clearly. Thanks for the education (although the term DB-9 should also be used in the description somewhere with brief explaination...due to suppliers not really understanding this idea either).

It should also be obvious that I was not using the Wikipedia content as source material for this module. I will try and do some cleanup as well based on that source. If you add anything from other sources, make sure that you note it on the external references area (even from dead-tree sources...include ISBN number instead). Rob Horning 8 July 2005 18:04 (UTC)

• According to http://www.lammertbies.nl/comm/info/RS-232_specs.html and http://www.arcelect.com/rs232.htm the last sentence in Databits has to be changed in:
  

The least significant bit (LSB) is transmitted first in this sequence of bits to form a character.

Thanks for the tip with the LSB/MSB change. That was an oversight on my part, and in retrospect, it should have been obvious. It also makes all forms of RS-232 data compatable at least on the bit level to start with, where the format of the bits is the same for all bit size transmissions except for just the number of bits actually transmitted. A logical way to organize the protocol. That and a simple mistake in the writing, so thanks for catching the mistake. --Rob Horning 09:07, 26 October 2005 (UTC)

Merging

What is the purpose of merging this module with the almost empty module Serial Programming:RS-232 Technical Manual (less then ten sentences in the module)? Shouldn't the almost empty module better be removed and references to it replaced with references to this module?

As the original author of this module, I strongly disagree with the premise that this module should be abandoned in favor of another Wikibook. There is a purpose and goal that I have in mind, particularly that I've put into the introduction to this Wikibook. This is a multi-chapter book about serial data programming, which the RS-232 Technical Manual is really a totally seperate item. This is not Wikipedia where you can have one and only one article about a particular subject. IMHO, a separate Wikibook that goes into even more depth would be useful, although one I'm not willing to write at the moment.

This other Wikibook started as a part of an editorial conflict me regarding the direction of this Wikibook about serial programming. I am not making a Wikiproject that points to serial programming references, but instead I'm trying to write a book. This distinction is somehow lost on some people, and don't understand the differences between Wikibooks and Wikipedia. As a book, I am trying to go into detail about a subject, and build on that knowledge in subsequent chapters. This is not an easy thing to do, although I am grateful for all of the assistance that has been rendered so far to improve these chapters I've already written.

In short, I don't see why the two Wikibooks can't be made for this subject. The Technical Manual is to be more of a reference guide, and this Wikibook is to be an introduction to the subject. In short, I am trying to teach about serial programming, and it is my intention to turn this into a textbook. Those are two very different goals and need to be written very differently. That they may have some similar content is besides the point. --Rob Horning 17:00, 15 October 2005 (UTC)

Where is it? (Hardware flow control description)

This is a part of the "Hardware" flow control protocol that will be explained below

At least the checked URL ? Two URL's below tells opposite voltage's meaning "stop" and "go".

http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html

http://www.taltech.com/TALtech_web/resources/intro-sc.html#Synch

PS: This seems to claim 0=go, 1=stop also, but it is not said frankly: http://www.hw-server.com/rs232_signals.html#t6

I guess I need to simply pull out an oscilloscope and find out for myself with a difinitive answer from the real world. I would venture to bet that both + voltage and - voltage being asserted as a logical "1" does occur. --Rob Horning 12:55, 5 March 2006 (UTC)