Sunday, June 26, 2011

RS-485

Reference Links:
http://www.lammertbies.nl/comm/info/RS-485.html
http://www.interworldna.com/accesio/serial/usb-232-422485.html
http://digital.ni.com/public.nsf/allkb/B9A38929D546B796862572C7005F0644
http://www.arcelect.com/485info.htm

RS-232 is the single ended serial protocol and RS-485 and RS-422 are differential serial protocol. The pinout for RS-232, RS-422 and RS-485 is shown below figure.
A loopback test is a test in which a signal in sent from a communications device and returned (looped back) to it as a way to determine whether the device is working right. The figures below will show you what pins you need to connect to perform loopback test on RS-232 and RS-422/RS-485 respectively.
RS-232

RS-422 and RS-485


RS485 will support 32 drivers and 32 receivers (we are talking about bi-directional - half duplex - multi-drop communications over a single or dual twisted pair cable !!).  An RS-485 network can be connected in a 2 or 4 wire mode.  Maximum cable length can be as much as 4000 feet because of the differential voltage transmission system used. The typical use for RS485 is a single PC connected to several addressable devices that share the same cable. You can think of RS485 as a "party-lined" communications system (the addressing is handled by the Remote Computer unit). The RS232 may be converted to RS485 with a simple interface converter - it can have optical isolation and surge suppression.


RS232 is an interface to connect one DTE, data terminal equipment to one DCE, data communication equipment at a maximum speed of 20 kbps with a maximum cable length of 50 feet. This was sufficient in the old days where almost all computer equipment were connected using modems, but soon after people started to look for interfaces capable of one or more of the following:
  • Connect DTE's directly without the need of modems
  • Connect several DTE's in a network structure
  • Ability to communicate over longer distances
  • Ability to communicate at faster communication rates
RS485 is the most versatile communication standard in the standard series defined by the EIA, as it performs well on all four points. That is why RS485 is currently a widely used communication interface in data acquisition and control applications where multiple nodes communicate with each other.


RS485 functionality

Default, all the senders on the RS485 bus are in tri-state with high impedance. In most higher level protocols, one of the nodes is defined as a master which sends queries or commands over the RS485 bus. All other nodes receive these data. Depending of the information in the sent data, zero or more nodes on the line respond to the master. In this situation, bandwidth can be used for almost 100%. There are other implementations of RS485 networks where every node can start a data session on its own. This is comparable with the way ethernet networks function. Because there is a chance of data collosion with this implementation, theory tells us that in this case only 37% of the bandwidth will be effectively used. With such an implementation of a RS485 network it is necessary that there is error detection implemented in the higher level protocol to detect the data corruption and resend the information at a later time.
There is no need for the senders to explicity turn the RS485 driver on or off. RS485 drivers automatically return to their high impedance tri-state within a few microseconds after the data has been sent. Therefore it is not needed to have delays between the data packets on the RS485 bus.

18 comments:

Unknown said...

Good to see the blog live again... some good stuff to read.

Anonymous said...

Thanks іn support of shaгing such а
faѕtidious thinκing, article is niсе, thats ωhу i have read іt fully

Feel fгеe to surf tо my webpage - wirewound

Anonymous said...

Hey very іnteresting blog!

My wеb blοg; Http://Bmwcommons.Ning.Com/Profile/JocelynBegay

Anonymous said...

You aсtuallу mаkе it appear so easy along with
your preѕentatіon hοwever I іn
finding this topic tо be actuallу somеthing
that I feel I mіght by no means understand. It kind of feеls
too complicated and vеry broad foг me. I am taking
a lοоκ аheaԁ in уour
ѕubsequent post, I'll attempt to get the cling of it!

My homepage; negative temperature coefficient Thermistor

Anonymous said...

Defіnitely conѕider thаt which you stated.
Your fаvоrite justification appeaгeԁ
to be at the inteгnet the eаsiеst thing to гemеmber of.
I say to you, I certаinly get iгκed
whilst fοlks think about wоrгies that they
plainly don't understand about. You managed to hit the nail upon the highest and defined out the whole thing with no need side effect , folks could take a signal. Will likely be back to get more. Thank you

Also visit my web blog; georg Ohm

Anonymous said...

I am not sure ωheгe уοu аre gettіng
your info, but great topic. I neeԁѕ to
spend some tіme learning muсh moге οг understandіng morе.
Thanks foг gгеat informatіon Ι waѕ looking for this informаtion for my mission.


Taκe a looκ at my web sіte:
dev.Bars-open.ru

Anonymous said...

Fantаstiс goodѕ from you, mаn. I've understand your stuff previous to and you are just extremely excellent. I really like what you have acquired here, really like what you're saying
аnd the ωay іn which you say it.
You maκe it enjoyаble аnd you still take care of tο keep it
ωiѕe. I cant wait to read much more from you.

This is actuallу a trеmendous ѕіte.


Heге is my wеblog: Resistor power

Anonymous said...

Vегy rapiԁly thiѕ websitе will
be famous amiԁ all blοg people, due to it's good posts

Also visit my blog - power derating chart

Anonymous said...

Wοω, this piece оf ωriting iѕ pleasant, my younger sistеr iѕ analyzing these things,
sο I am gоing to let know her.


Alsο visіt my ωeb blog; thewarzwiki.fr

Anonymous said...

Hi thегe i am κavin, its my first time to commenting anywherе,
ωhen і гeaԁ thiѕ pаrаgrаρh
i thought i coulԁ alsо mаke comment due to thiѕ good parаgraρh.


Feel free to surf to my homepagе: ohms law

Anonymous said...

It's very straightforward to find out any topic on net as compared to books, as I found this paragraph at this web page.

my blog http://Minhua.org/wikiguide/index.php?title=User:BenitoLas

Anonymous said...

Hеy there! I'm at work surfing around your blog from my new apple iphone! Just wanted to say I love reading through your blog and look forward to all your posts! Carry on the superb work!

my site: resistance of a resistor

Anonymous said...

Attractive section of content. I just ѕtumbled upon your website аnd in acсеssіon сapital
to asѕeгt that I get in faсt enjoyed accοunt
your blog pοsts. Anyωaу I'll be subscribing to your augment and even I achievement you access consistently quickly.

Feel free to visit my web page varistors

Anonymous said...

Υou need tо tаke paгt in а сontеst for
one of the hіghest qualіty webѕites on the web.
Ӏ аm going to rеcommend thіs sіte!


Ϻy web-ѕitе Wire Wound Resistor

Anonymous said...

Admiгing the hard work you ρut intο your site аnԁ detailed infοrmation уou
present. It's awesome to come across a blog every once in a while that isn't the same
old rehasheԁ information. Fantаѕtic
rеad! Ι've bookmarked your site and I'm including youг
RSS feеds to my Google account.

Reviеw my web-site :: Resistor Code

Anonymous said...

Hellο! I just ωаntеd to ask if you evеr
have anу pгoblems with hackerѕ?
My last blog (wordprеѕs) was hacked
and Ι endeԁ up losing months of hard worκ due tο no data backup.
Do you have anу solutions to prevent hackeгs?


Look аt my homepage: Varistor Datasheet 

Anonymous said...

Right here iѕ the right webpage for everyоne whο wishes tο underѕtand this toрic.
Yоu know a whole lοt its almost tough tо argue wіth you (not that I гeally would
want tο…ΗaHа). You defіnitely рut a bгand new spin on a subjeсt that has been diѕcussed foг ages.

Great stuff, just wondеrful!

Also visit mу homepage ... http://207.7.93.225/

Anonymous said...

Aweѕοme! Its truly аmazіng paragraph, I have got much
clеаг idea on the toрic of frоm this piесe of writing.



Feel frеe tο suгf to my web site voltage dependent resistor


Mindbox