RS233 RS485
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Thread: RS233 RS485

  1. #1
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    I have an RS232 to 485 converter so I was thinking the 9 pin com port on my computer was the RS232 and the phone jack end was the 485 part. I would like to hook up to a Trane UCP and it had a jack that said RS232 but looked like a phone jack. Is a serial port a RS232? What would I need to hook up to Trane?


    What is the difference in RJ11 RJ45 and a regular phone jack?

  2. #2
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    Originally posted by incontrol
    I have an RS232 to 485 converter so I was thinking the 9 pin com port on my computer was the RS232 and the phone jack end was the 485 part. I would like to hook up to a Trane UCP and it had a jack that said RS232 but looked like a phone jack. Is a serial port a RS232? What would I need to hook up to Trane?


    What is the difference in RJ11 RJ45 and a regular phone jack?
    It is likely that you are correct that the 9-pin connector on the back of your computer is indeed an RS-232 port. And that the RJ11 connector is the RS485 business end of your converter.

    But let's clear up a few things.

    When you're talking about things like a DB9 (or DB15 or DB25) connector, or RJ11 (or RJ45, etc) type connectors, all you are doing is talking about connectors. The physical construction of a device used to connect wires
    together. Saying things like DB9, DB25, RJ11, RJ45, etc say nothing whatsoever about what the wires connected using those "connectors" are doing.

    By using a connector name, or a specific type of connector, you are not saying anything whatsoever about what the wires are for, or what they're doing.

    Now, simply by convention, the usual method commonly implemented by computer manufacturers, most often if yah see a male DB9 connector on the back of a computer, it's "usually" an RS232 port. But there are no rules or laws about this. If the manufacturer had wanted to use a DB9 type connector for some other purpose, whatever purpose, manufacturer could do this. And sometimes
    does, not often tho, as they don't want to confuse a customer.

    The same goes with RJ11 connectors. Or most any other sort of common connectors.

    A DB9 connector does NOT automatically mean something is an RS232 port. Likewise, an RJ11 does NOT automatically mean it's a "phone jack", nor does RJ45 automatically mean it's a "lan" connection. Although, those are the most
    commonly used connectors for the respective purposes. A maker of equipment could just as easily, and is free to do so, use a terminal board connector. Or some other sort of connector altogether.

    Okay?

    ie The RS232 to RS485 converter I use most times has a female DB9 connector on the RS232 side and a terminal board connector on the RS485 side. That's simply the choice of the maker of that particular converter (B&B). If I need some other arrangement on the RS485 side, I simply run to Radio Shack and buy the corrrect blank connector, connect wires to it in the right order as required by the maker of whatever it is I want to "talk" to, and thus make my own wiring harness converter.

    The terms RS232 and RS485 do not specify a particular type of connector which must be used. Those terms are used to specify what kind of electrical signals are to be used to represent a "1" or a "0" data bit, what voltage levels, and a whole host of ther electrical characteristics for those communications protocols. I'm not gonna get specific, as the "standards" which specify everything having to do with implementing RS232 or RS485 communications are each a whole book in their own right. And it's really not necessary for most folks to know all the details unless you're planning to design communications circuit boards and chips.

    A somewhat simplified explaination.

    Typically, the most of used and included method of serial, one bit ... a 1 or a 0 ...sent and received at a time, communications used on computers for communication with other devices is RS232. Using a DB9 connector. This method
    has been around a long time, since before personal computers. RS232 standards "allow" for a lot of different wires to be used, each with specific purposes. But in most cases not all of them are used.

    In fact, most often, only 3 wires are used on that DB9 connector. Even those there are other wires hooked up to the various pins inside the computer. The 3 wires mostly used are "Transmit", "Receive", and the 3rd wire is ground. The RS232 "standard" calls for all signals to be referenced to a common ground. In general, to talk to another device with a RS232 port, the "transmit" wire from device A is connected to the "receive" wire of device B, and vice versa. Both have ground connected in common. Most implementations of RS232 only allow PTP communications. That's Point To Point. In short, just two devices on the comm line.

    RS232 is simple to implement, cheap, and an included communications method built into a LOT of things. But it has some drawbacks. It's relatively slow,not very immune to noise or interferance, and typically not useable for
    distances greater than about 50 foot. Not without using additional circuit boards.

    RS485 has been around a long time, too. But isn't usually included on things like personal computers. Circuitry is more complex and more expensive, and the description and specifications for this communications method allows for a lot more flexibility. But that flexibility comes at added expense. And back in the early days of computers, no one thought there was any particular reason a personal computer user would need the extra abilities of the RS485
    communications protocol. So it's not usually found on personal computers. But it is used a LOT in industrial and equipment control.

    RS485 is most often implemented using 2 wires, usually a twisted and shielded pair. Signals, determining if a "1" or a "0" is being sent, is not done by comparing voltage to a common ground as in RS232. Its done by comparing
    relative voltage between wire A and wire B. ie If the voltage of wire A is 200 millvolts greater than wire B, a "1" is being sent. Or, if voltage on wire B
    is 200 millivolt, or greater, than wire A, a zero is being sent.

    Something like that, I'm operating here off memory. And it's been a long time since I've studied the subject.

    Also, RS485 can have a voltage range of from -7 volts to +12 volts.

    Net result, RS485 communications is more resistant to induced, transient noise than is RS232. And can "talk" over much greater distances. Typically, around
    4000 foot or better without repeaters or anything else special. The reason the communications method is popularly used in a lot of industrial and commercial controls and equipment.

    Also, the RS485 specs cover more characteristics of that communications protocol. Setting up specifications and standards that allow RS485 communications to "network". That is, on a RS485 bus, you can have more than 2
    devices. You can have a bunch. Typically, one device will be declared the "master" and the others will be "slaves". Master controls and asks questions,slaves only "talk" when spoken to and given permission by the master. In RS422,
    which is electrically similar to RS485, this is typically the only arrangement. And/or, slaves can listen only and never speak. But with RS485, you can have more than one master. They just have to know about each other, and you need to specify the order of "token" passing (the order in which each master will take turns controlling the network), the timing for how long each may be a master, and who is the primary master when things go wrong and the network gets
    interrupted, token lost, and everything has to start over again and somebody has got to be first, to keep things from getting confused. In RS485, each device has a definite network "ID", and all the slaves listen when the master
    speaks, but only the slave addressed in the message may speak in response.

    Okay? Get the differences? There is a lot of other stuff involved. But those are the important points.

    Now, as concerns the RJ11 jack and connecting it to the Trane unit. Was the converter made specifically for Trane devices? If not, then you don't know which pins are used, and which wires are connected to which pin. There really
    are no "industrial standards" for this. ie, in devices which use RS232 and a RJ11 connector, and I work with many, I have to have a small collection of RJ11 connectors because different makers of this or that have put the "transmit" wire on one pin, and the "receive" on another, as compared to other makers of other equipment also using RS232 and RJ11 connectors.

    Sometimes I get the info from the manufacturer (most of the time), other times I've had to resort to breaking out an analyzer and figuring it out the hard way. ie When having to work with obsolete stuff. Or when a manufacturer wants to charge me $200 for $1 worth of wire and connectors. I don't mind paying reasonable amounts, but some makers of equipment get ridiculous about this sort of thing. And just piss me off. So I make an end run around em. But don't like doing this as it takes valueable time.

    Anyway, if your converter was not specifically made for talking to Trane devices, pins connections may or may not be right. Plus, you need to know the actual "data packaging" protocol used by Trane if they're not using standard, plain vanilla ASCII. ie, The package, or sequence of data required so that the device understands what you are saying, what you want, and whether or not you'
    re talking to it. For example, one series of devices I talk to requires a packet in ASCII that includes the network ID of the device being addressed, a specific 2 byte code that tells addressed device whether you're requested a
    read or a write, 4 byte code specifying item, another 2 bytes specifying which attribute of item you're talking about, 4 null bytes if it's a read or 4 bytes of data if it's a write. And BTW, the bytes for memory address and values are in reverse notation.

    In short, it's usually a lot easier to just contact a manufacturer and get their software to do the talking with, and to get their pin-out directions if they'll tell you that as versus insisting that you buy interface from them
    specifically.

    These things can be figured out without manufacturer info or support. I've done it, but it's a royal PIA. Rarely worthwhile, unless you're just a hobby hacker like I am. I started doing this sort of thing just for fun, and just on old and obsolete stuff that maybe I wanted to do something with. In my worklife, as a matter of making money, almost never a worthwhile venture. Simpler, easier, to just buy manufacturer's software.

    Tho, if the maker includes some sort of ASCII mode builtin interface on the chips in the controller, just a matter of figuring out which pin connects to what, then start up a terminal program, play with basic settings (start with baud,8,N,1), and hit keys randomly to see what response you get. Analyse results.

    But I'd surely not do this witrh a customer's equipment, unless yah feel like buying the replacements. You could inadvertantly screw some things up royally. If you're not just playing with an old controller, I'd contact Trane, or see if one of the guys on this forum knows specifically about the controller you're interested in and has info for you.

  3. #3
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    Austin
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    WOW!!!!!!!

    We've just been schooled!!!! And I mean that with the utmost respect...thanks osiyo!!!

    Now, as to incontrol's question...we need to know what Trane system you want to hook up to. If it is a Tracker, is it earlier than version 12? If it is Tracer Summit, is it earlier than version 13? Is it Tracer 100 or L? Every single one of those has a different requirement for local communication. Give us more info and we will be able to help you out.

    osiyo, you have way too much time on your hands if you can give responses like that...but they sure are informative...WOW!!!
    Def. of insanity: doing the same thing over and over again expecting different results!!

  4. #4
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    Jul 2002
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    Thanks Osiyo. I did suspect it was a protocol. Now if I usually use a 6' 9 to 25 pin to hook up but want to put the computer far from the controller, what would be the best way since you say ~50 feet for RS232?

    TS It was freezing on the roof so I didn't pay too much attention. Checked my notes and found the following numbers although they may be from something else.
    PCCB-BDFBHBOBAA
    CPL2997-2865-01

  5. #5
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    the only truly universal rs232 to rs 485 converter I have found is the telebyte model 366, it has a small display that shows where the data bit is on the wave form as well as other info. You connect it on to an operating rs485 loop and watch the display then set the dip switches accordingly. It has worked great with carrier comfort net, trane everware, and summit, allerton, and american auto-matrix systems. It is a little iffy with johnson metasys but i suspect I had a faulty controller that i was trying to get into. Telebyte builds the adapter for trane's everware and rover packages. Eirc

  6. #6
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    Originally posted by incontrol
    Thanks Osiyo. I did suspect it was a protocol. Now if I usually use a 6' 9 to 25 pin to hook up but want to put the computer far from the controller, what would be the best way since you say ~50 feet for RS232?
    You want to be farther than 50 foot away?

    RS232 "MAY" work farther than 50 foot. The 50 foot thing is a general rule of thumb. Actual distance possible is gonna depend on how much EMI (electrical noise) is around, quality of the wiring used for the connection, and just how good the communications chips are at each end. Not all I/O chips are the same. Depends on the engineering skills of the component manufacturers, and quality of parts they used.

    But since you say you have an RS232 to RS485 converter. What's the problem? Plug RS232 end into your computer, and add extender wiring to the RS485 end.

    Or am I missing your point?

    FWIW, if you're talking about something different than the original RS232 to RS485 converter you were originally discussing. You can buy RS232 extenders (sometimes called repeaters). Often this is nothing more than a pair of RS232 to RS422, or RS232 to RS485 converters, in between which you can string some long wiring. ie 4000 foot or so.


  7. #7
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    We normally have a computer set up by the controller with a 9 to 25 pin. Guy wants the computer upstairs in his office but the controller has to stay in the boiler room.

    ESDD I think you answered my next question. I was looking at https://hvaproducts.com/secure/ViewItem.aspx?PID=15828 a Johnson AS-CBLPRO-2 and was wondering if it is a glorified 232-485 converter. You can hook up to Johnson with a generic converter?

  8. #8
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    Johnson's CBL-PRO2 is not the choice tool for 232-485 connections - it's used to hook up your laptop's serial port to Johnson's Zone Bus, which is quite slow compared to communication on the N2 bus via a real 232-485 converter...
    The Johnson 232-485 converter you might use is the MM-CVT-101. One of its drawbacks (other than its price) is the fact that it requires external power. You commonly find yourself on a rooftop without the NEC-required convenience outlet within extension cord range, and even though the laptop may run just fine for awhile on its batteries, you'd be out of luck trying to power the converter.
    Hence the need for what you call a "generic" converter. ESDD already mentioned the Telebyte 366 (and I've successfully used both the 366 and the 365), but alas, they too require external power. The advantage of that means of powering it is the isolation available (hate to cook that expensive laptop's serial port with a stray signal).
    The B&B Electronic's 485SDB9TB converter is our company's converter of choice:
    http://www.bb-elec.com/bb-elec/liter...9tb-3803ds.pdf

    We find it robust enough for field use, it doesn't require all sorts of dipswitch changes for use with the three or four brands of controllers we most commonly connect to, and is powered off the serial port, so no need for 120V.
    ESDD was correct, however, in that the only truly universal converter is Telebyte's 366. The above mentioned B&B converter is half-duplex two-wire only. If your system requires full-duplex four-wire, go Telebyte, and bring your extension cord. If you need to communicate only over two-wire busses like N2, go B&B.

  9. #9
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    RS-485 Repeater

    Little something to add...

    You can use the repeater listed below on the johnson N2 Bus.

    http://www.bb-elec.com/bb-elec/liter...5OP_2004ds.pdf

    set it up as half duplex.

    The B&B converter is about a third of the cost of the Acromag that Johnson reccomends.

    however you are getting what you pay for the Acromag has alot more on board options that can assist in troubleshooting the network.

    Allen

  10. #10
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    The only controlls package I've sucessfully communicated to with the B&B converter is the Carrier package thats why I went with the Telebyte unit. True it requires an external power source, but I've found that a 9v battery and a mini power jack works well for about 4 hours. The Carrier package carries the data in a different point on the wave form than the Trane packages, thats why the telebyte 366 is so usefull.

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