Plc & Computer Communication

I am very confused after a lengthy search of the allen bradley website and other online information regarding what is the easiest way to connect a SLC 500 to your computer.

Let me tell u what I have learned first.

More advanced processors have more communication options. Almost all PLC CPU's (same thing as a processor) have the DH 485 ports. Your computer has a familiar USB port.

So how do u connect the computer to the PLC processor? Well...hmm....

Is there such thing as a cable that has one end DH 485 and the other USB? I think the answer is no. Your computer needs to "interface" before it can talk to (communicate) with the PLC processor.

So what do you do? There is an expensive 1747 PIC controller, and it allows networking of multiple computer stations.

But if your doing this to learn like me, for fun...then why not investigate the 1747 UIC? It is a device that connects to your computer with a USB, and it has a little switch to let u select the DH-485 port or the big ugly RS 232 port. An RS 232 port has many pins and 2 screws to hold it to the cable. But forget the RS 232 port, just use the DH-485 because almost all processor types (SLC 500, 5/01, 5/02, etc.) use this.

Then the cat 5 or the more expensive allen bradley 1747 C10 cable connects from the UIC's DH-485 port into the processor's communication port.

Ok thats what I know. Probably there are errors in my logic.
First off, check out

http://www.plctalk.net/qanda/arch/topic/6991-1.html

This is where I found out that an ordinary CAT 5 cable would work instead of letting allen bradley do what they do best - rip you off-

Ebay sells cat5 cable, retailing for approx. 3 dollars CA
allen bradley sells 1747-C13, retailing for approx. 50 dollars CA

Question 1.Is this right? Is CAT 5 cable ok to use?

Question 2. Is there such thing as a cable that has one end DH 485 and the other USB? Is any computer/PLC processor interface even necessary?

Question 3. Is the PIC better for only using one computer to control small PLC applications, example: one PLC with a small power supply, one processor, and only a few I/0 cards in the same rack? Or is the UIC mentioned above a good choice?

Question 4. Please suggest any other thing I need to know about communicating with a PLC.

Question 5. What are your feelings about buying I/O cards off of ebay? They are cheap, but no manuals, specs, wiring diagrams? I guess its pretty much plug in the modular processor, I/o card, etc and go. plug and play in other words?

Question 6. Is there anyone who has tried using the 1747 UIC? Why did you buy it instead of connecting it in the more common PIC communication method?

Processor info:
http://literature.rockwellautomation.com/idc/groups/literature/documents/br/1747-br007_-en-p.pdf

Thanks for any help!!!!!!!!!!!!!!!!!!!!!!!!

Andrew

please reply even if u can only answer one of the questions. thanks.

Greetings Andrew,

first of all ... exactly what type of processor do you have? ... yes, there IS an SLC-500 available ... it is commonly called an SLC “brick” ... but to add to the confusion, the term “SLC-500” is also commonly used as a “family name” to refer to any of the following “modular” type processors:

SLC-5/01; SLC-5/02; SLC-5/03; SLC-5/04; or SLC-5/05 ...

if you have anything from an SLC-5/03 or up, then the RS-232 serial cable is definitely the way to go ... especially if you’re doing this for “fun” or learning purposes ...

what is the easiest way to connect a SLC 500 to your computer.

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again ... we need to know exactly what model processor you have ... the best thing to do is to post the “catalog” number ... the answers below are given in general terms (since we’re not sure what processor you have) ...

Question 1.Is this right? Is CAT 5 cable ok to use?

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no ... just the CAT 5 cable is not enough ... that’s just one piece of the puzzle ... you will need some type of “adapter” like the 1747-PIC ...

Question 2. Is there such thing as a cable that has one end DH 485 and the other USB? Is any computer/PLC processor interface even necessary?

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no ... not just a simple cable ... there is “magic” inside the “adapter” ... for one thing, the voltage levels used by the computer are different from those used by the processor ...

Question 3. Is the PIC better for only using one computer to control small PLC applications, example: one PLC with a small power supply, one processor, and only a few I/0 cards in the same rack? Or is the UIC mentioned above a good choice?

Click to expand...

if your computer has a built in serial port, then the PIC is a good choice ... if your computer has only a USB port (no serial), then the UIC is a good choice ...

Question 4. Please suggest any other thing I need to know about communicating with a PLC.

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if you have an SLC-5/03 or higher, then the serial port is the way to go ... it’s cheaper (you can build your own) and I don’t know ANYBODY who actually fools around with those little screws on the cable for just “programming” purposes ... maybe for a permanent field installation ... but not for just messing around in the lab ...

Question 5. What are your feelings about buying I/O cards off of ebay? They are cheap, but no manuals, specs, wiring diagrams? I guess its pretty much plug in the modular processor, I/o card, etc and go. plug and play in other words?

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with Allen-Bradley and most other brands, the lack of manuals is NOT a problem ... you can easily find that type of stuff on the AB website ... if the seller on e-bay is well-established then you should have little or no problems ... but ... before you buy anything, ask around at the maintenance department of some local PLC users ... basic idea: when one or two inputs or outputs “go bad”, some shops just throw the old modules on a “junk” shelf ... if you’re lucky, they might just let you have a sample that is useless to them but would work perfectly for someone who’s just experimenting with a few inputs and outputs ... this “ask around” approach could have the added advantage of getting you a “foot in the door” to an actual PLC user ... strike up a conversation about what you’re trying to learn – and why ... you never know where something like that can lead in the future ...

good luck ... and welcome to the forum ...

and one more thing ... you DO have copies of the RSLogix500 and the RSLinx software available ... right? ...

here is an XLS file with all the different cables used by AB. the 1747 UIC allows communication to the rs 485 to USB with the assistance of the proper cable. If your using USB then the 1747 Pico controller does you no good. for rs 232 to USB I've found that the standard usb converters work with the AB cables.

smfula said:

Question 4. Please suggest any other thing I need to know about communicating with a PLC.

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Maybee one more thing.

If you just start to deal with automation, you have to realize that AB have these communications protocols because they really are the best.

An also, Mitsubishi has a different set of protocols because they really are the best.

An I should reaaly point out that Omron has his sets of protocols because they really are the best.

You get where I'm leading you? Have fun and welcome!

smfula said:

It is a device that connects to your computer with a USB, and it has a little switch to let u select the DH-485 port or the big ugly RS 232 port. An RS 232 port has many pins and 2 screws to hold it to the cable. But forget the RS 232 port, just use the DH-485 because almost all processor types (SLC 500, 5/01, 5/02, etc.) use this.

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Don't knock the RS-232 port. It's the one of most consistent things in automation. It seems like 90% of the hardware out there, EXCEPT laptops, comes with RS232 on it somewhere. It's a good fall-back and it's cheap (unless you're ordering custom cables). Not to mention, the data stream is easier to monitor, manipulate, or emulate when you're sitting on the plant floor (ambient temperature 100 deg. F), and wondering what the heck is up with your communication. There's no subnet, VLAN, domain controller, firewall, or IT policy to get in your way, either.

Of course, if you read everything in the previous paragragh while you're wearing your management hat, you'll see that there may be some security holes. On the other hand, you'd actually have to plug into most RS232/485 networks first, rather than locating them by random chance over the internet.

AK

WOW!! This site is amazing. I actually recieved a reply--actually numerous replies! I never knew there were people out there interested in PLC's. plctalk.net is now under favorites. thank you everyone

These comments are based on who replied first.

akreel-

I appreciate your advice on the RS-232 port. I did not know 1)that it "bypasses" (?) firewalls and security programs for simple communication, 2) that it is used so much in industry.

my assumption was USB is the latest and greatest, and those big ugly pin connectors are becoming outdated. This is generally not true. Your advice is appreciated.

Pierre-

Not sure If I agree with you. I think some components are interchangeable, and heck if a cheap CAT5 cable does the job of a 50 dollar 1747 C10 communication cable, then Im inclined to go the cheap route. Maybe I will eat my words if my "USB-to-DH-485 Interface Converter" (that I am planning to buy) gets fried or causes problems.
Your reasons were not specific as to why I shouldn't try the CAT5 cable. Thanks for your advice anyways!

mordred-


Presently I am unable to open this XLS file, but will attempt later to fix this problem. I have read your reply numerous times, please if you have time, clarify a few things for me.

You said "the 1747 UIC allows communication to the rs 485 to USB..."

I think you ment to say "rs-232" but no big deal. Yes, that makes sense, the 1747 UIC is the interface between the computer (USB port) and the PLC processor's port, either the (RS-232) or (DH 485).

You said "with the assistance of the proper cable"

From the 1747 UIC converter device, I plan to use a CAT5 cable (unless Pierre can convince me otherwise) or I suppose I could use the RS-232 cable with two female ends. I guess from what akreel said, the RS-232 option is better?

Ron-

Thanks alot for the effort in this reply. I hope you might feel able to answer a few questions before I begin to purchase my own PLC system.

Your explaination of PLC 500 is good, I forgot that PLC 500 applies to all types of processors (a catch all phrase) even though it is also a processor.

My dad has a barn that needs to be updated, and it contains a simple mill for grinding feed, a few sensors, limit switches, trip rods, (about 14 inputs) and 7 AC motors (outputs)

My idea is to prototype a PLC in my lab/bedroom, using little lights to simulate the operation of the milling system. There is 5 motors, all 120V and one 240V (7.5 A) motors.

You probably dont care about the application, but basically I thought Id mention it and perhaps you would suggest an appropriate processor type.

My option is to buy either a 5/03 (or better) that allows the RS-232 cable connection and the DH-485 cable connection, or buy a slower processor; a 500, 5/01, 5/02 that permits ONLY the DH-485 cable connection.

I have no clue what processor to buy. I dont need fast response time or much memory. Why not a 5/02? or a 5/01? I dunno...your suggestions would be really appreciated.

Mordred seems to think the Pico controller (PIC) is not useful in my application. You say I need one. This is a conflict in advice, so hopefully someone will resolve this issue. My opinion is unchanged-forget the PIC and use a 1747 UIC "USB-to-DH-485 Interface Converter" as found at the following website:

http://www.rockwellautomation.co.uk/enews/usb_dh_485.htm

Again, PICs are great for big networks in huge factories that churn out millions of widgets per day, but for me, with one computer and one small PLC, (that I hope to buy) I think the 1747 UIC is the best bet.

My question #2 was probably stupid, and thanks for being kind! lol but I now am fully aware that PLC's operate on a different voltage level and some form of interface is necessary. So far I have investigated two options, the PIC and the 1747 UIC.

Pertaining to #3, if I have a serial port from my computer, do I need a PIC? I think its cheaper to forget the serial port on the computer, and forget about the PIC. Instead, use the USB on your computer, and use the 1747 UIC converter that connects through a cable to the processor of the PLC. Is that too simple? The website listed above directly states that you can connect it to the processor, and there is no mention of a PIC.

In question #4, you can build your own what? serial port? huh..i dont get it. I am misunderstanding this. Maybe you mean the serial port,
(RS-232 connection), connects to a cheaper cable type.

The last question, was relating to ebay purchases. I now realize that I may unknowingly purchase a faulty or partially faulty product. Your example of an imput card with one or 2 bad imput terminals was helpful. Hopefully I'll be lucky and get a good one, and if im not then I dont care, as long as I have enough I/O's to experiment with PLC's and eventually implement the system in my dads pig feed mill.

If any of you folks want to reply, I would appreciate it and hopefully someone else also is encountering these issues with PLC communication. Thanks this site is really GREAT!

Have you looked at the micrologics yet??? It sounds like all your going to have is Discrete I/O's.. Just a thought.

My option is to buy either a 5/03 (or better) that allows the RS-232 cable connection and the DH-485 cable connection, or buy a slower processor; a 500, 5/01, 5/02 that permits ONLY the DH-485 cable connection.

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I would buy the 5/03 or better, but that's just me. Then go to Rat Shack or eBay and get a Null Modem DB-9F to DB-9F cable and you are set. On 2nd thought, get a straight through cable + null modem adaptor. That way you can use the cable for talking to a Panelview as well, if you so decide to do so in the future.

Also, the 5/03 and above support more advanced instructions.

You do not need a PIC to do serial (RS232), only for DH485. 5/03 is capable of doing DH485 and/or RS232.

Also, there are other, cheaper alternative then AB/Rockwell stuff. The $1500+ for softwares is a bit steep just for playing around. Unless you have your sight set on a career in PLC in which case learing AB in North America would make sense because of their market share.

RSLinx "lite" comes together with RSLogix500.
So you dont need any other software than RSLogix500.

I would choose an SLC5/03.
This because it has a full instruction set, and because it allows online programming.
IF you dont need this, I would pick an ML1200.

If you pick the SLC5/03 then you need RSLogix500 and a 9-pin to 9-pin null-modem cable: 1747-CP3.

If you pick the ML1200 then RSLogix500 "starter" will be enough. The limitation of "starter" is that it does not allow online programming.
You will also need a cable with an 8-pin mini-DIN plug in the other end: 1761-CBLPM02.

smfula, I think you've gotten some good answers regarding the usability of DH-485 networking.

I'd like to add a couple of statements.

Statement 1:

RSLinx Lite software is free and is necessary to interface between RSLogix 500 and any SLC or MicroLogix controller. It is included with RSLogix 500 on the CD and is also downloadable at no charge. A-B separated the communications functions from the ladder editor years ago to accomodate multiple applications (RSLogix, PanelBuilder, RSView, DriveTools, etc) simultaneously having to communicate with the controller.


Statement 2: If you are using SLC-500 controllers and DH-485 networking, buy a 1747-UIC interface. It's the same price as a 1747-PIC and far easier to use. If you only need to communicate with one controller, get an SLC-5/03 and use the RS-232 port with an inexpensive "null modem" cable.


Statement 3: The DH-485 jack on an SLC-500 controller has +24 VDC present on some of the pins, in order to power some old-fashioned handheld programming devices and isolator devices. If you use the wrong cable, you will destroy the device that you plug into it. The A-B 1747-C13 cable has the exact correct pinout for this purpose, and you can fabricate one from the pinout available on the A-B Knowledgebase.

Addendum 1 to Statement 3:

I have used an ordinary Cat5E cable between an SLC-5/03 and 1747-UIC and it works with no problems and no damage.

Addendum 2 to Statement 3:

I know that if you used a "crossover" Cat5E cable between the SLC-5/03 and 1747-UIC it will not work and may damage the 1747-UIC or the controller.


Statement 4:

You can poison the tone of a lengthy post with just one insult. Try to keep your attitude positive and you will find that PLCTALK.NET is full of helpful members. Welcome !

Smfula the 1747-uic works great on the RS 485 connections. For example. Micrologix 1000 with 1761-cbl-pmo2 ser b cable as one example. However if you try the 1747-uic to connect to a micrologix 1200 on its rs 232 port it will not work even though the cable is the same. What I've ended up doing is using the same cable as mentioned above and used a standard rs 232 converter. in particular the MT609-2
conterter. The XLS file requires microsoft office to open. For that matter I've used the 1747-uic on an SLC 503 using a standard cat5 cable. To answer your other questions. RS linx supplies the drivers to run your communications. A driver is a software package used to run or configure a device. a good example of drivers is the software disks that you install when you change out your video card. As far as the 1747-UIC is concerned the main reason why it won't work in the above situation is that the DB9 connector on the UIC is RS 485 only. If you built a cat5 to 9 pin d shell it would probably work.

Greetings Andrew,

answers for your questions:

Your explaination of PLC 500 is good, I forgot that PLC 500 applies to all types of processors (a catch all phrase) even though it is also a processor.

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actually it’s SLC-500 (for Small Logic Controller) ... PLC is for Programmable Logic Controller ... this is larger (and more expensive) unit – common models are PLC-5/20; PLC-5/40; etc.

My dad has a barn that needs to be updated, and it contains a simple mill for grinding feed, a few sensors, limit switches, trip rods, (about 14 inputs) and 7 AC motors (outputs)

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it would be a good idea to nail down this list with “names” for the inputs and outputs ... and also the voltage and current levels involved ... you’ll need this information eventually ... the sooner you pull it all together, the better off you’ll be ...

My idea is to prototype a PLC in my lab/bedroom, using little lights to simulate the operation of the milling system. There is 5 motors, all 120V and one 240V (7.5 A) motors.

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not a bad idea ... but switches and buttons to simulate the inputs will turn out to be a lot handier than lamps for the outputs ... the output modules will already have little LEDs that will light up ... an external lamp is usually overkill ...

You probably dont care about the application, but basically I thought Id mention it and perhaps you would suggest an appropriate processor type.

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trust me ... we all care about the application ... remember, the PLC is just one part of the puzzle ... you can’t program the “brain” if you don’t know how the rest of the system functions ...

My option is to buy either a 5/03 (or better) that allows the RS-232 cable connection and the DH-485 cable connection, or buy a slower processor; a 500, 5/01, 5/02 that permits ONLY the DH-485 cable connection.

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from the “speed” viewpoint, my guess is that any PLC would operate fast enough to control a barn ...

I have no clue what processor to buy. I dont need fast response time or much memory. Why not a 5/02? or a 5/01? I dunno...your suggestions would be really appreciated.

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if all you want to do is program the barn, then cheaper sounds better ... but if you want to be able to “learn more” and eventually “do more” then a little extra money invested up front is likely to pay off in more flexibility and power down the road ...

Mordred seems to think the Pico controller (PIC) is not useful in my application. You say I need one. This is a conflict in advice, so hopefully someone will resolve this issue. My opinion is unchanged-forget the PIC and use a 1747 UIC "USB-to-DH-485 Interface Converter" as found at the following website:

http://www.rockwellautomation.co.uk.../usb_dh_485.htm

Click to expand...

something is getting scrambled here ... a “PICO Controller” is a VERY small PLC ... specifically you can program it and use it to control small applications ... on the other hand, a 1747-PIC is a communications adapter ... it’s basically a plastic box full of electronics and fitted with two communications cables ... it is used to convert from RS-232 (at a computer’s serial port) to RS-485 (at the SLC’s RJ-45 port) ... specifically, you can NOT program it to control anything ... remember that I based all of my previous suggestions on “general terms” since we don’t know exactly which processor you’re going to buy ... and we don’t know exactly whether your computer will (or always will have) a serial port ... anyway ... I didn’t say that you “need” a 1747-PIC adapter ... I said that a simple “cable” will not work IF (big if) the PLC has ONLY a DH-485 port ...

Again, PICs are great for big networks in huge factories that churn out millions of widgets per day, but for me, with one computer and one small PLC, (that I hope to buy) I think the 1747 UIC is the best bet.

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the decision of whether to use a 1747-PIC or a 1747-UIC has NOTHING to do with big networks” or “daily throughput” ... the only consideration is whether your computer has a built-in serial port or only a USB port ...

My question #2 was probably stupid, and thanks for being kind! lol but I now am fully aware that PLC's operate on a different voltage level and some form of interface is necessary. So far I have investigated two options, the PIC and the 1747 UIC.

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don’t laugh ... I know of several cases where people have “home brewed” their own communications cables and damaged either the computer’s or the SLC’s communications port

Pertaining to #3, if I have a serial port from my computer, do I need a PIC? I think its cheaper to forget the serial port on the computer, and forget about the PIC. Instead, use the USB on your computer, and use the 1747 UIC converter that connects through a cable to the processor of the PLC. Is that too simple? The website listed above directly states that you can connect it to the processor, and there is no mention of a PIC.

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you’re correct ... if the price of the UIC is not an issue, then that is by far the way to go ... sometimes you can find a used PIC on ebay for around $50 ... the UICs haven’t been around very long ... they seldom if ever show up used on ebay ...

In question #4, you can build your own what? serial port? huh..i dont get it. I am misunderstanding this. Maybe you mean the serial port,
(RS-232 connection), connects to a cheaper cable type.

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you can build your own serial cable ... pin 2 to 3 ... pin 3 to 2 ... pin 5 to 5 ... and you’re ready to go ...

The last question, was relating to ebay purchases. I now realize that I may unknowingly purchase a faulty or partially faulty product. Your example of an imput card with one or 2 bad imput terminals was helpful. Hopefully I'll be lucky and get a good one, and if im not then I dont care, as long as I have enough I/O's to experiment with PLC's and eventually implement the system in my dads pig feed mill.

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the suggestion was to ask around for FREE stuff to play around and learn on ... the stuff that you get on ebay will USUALLY work OK ...

I am planning to purchase the RSLinx and RSLogix software even if it is expensive. Not worried about the cost.

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your local distributor is going to LOVE that attitude ... I suggest that you get in touch with them soon ... they’ll be glad to help you with most of the questions you have ... even a free “test drive” for the software and a hardware “demo” (at their offices, of course) are usually well within the realm of possibility - if you’re pleasant and show an interest in buying things ...

Initially, I thought purchasing RSLogix was enough software. You connect your PLC to your computer using the 1747 UIC and thats it. I guess this RSLinx software is important?

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yes ... vital ... but as others have said, it comes free with the RSLogix500 software ...

Does it provides a 'driver' to allow communication from the computer to the PLC? That is the idea ive gathered from my web search of RSLinx. I dont really know what a 'driver' is. I cant find any websites that explain what it is. Someone explain please.

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coming fresh out of the box, RSLinx knows NOTHING about what type of equipment you’ll be using for your computer ... and it knows NOTHING about what type of PLC you’ll be using ... setting up the driver is a process of configuring (setting up) the software for the protocol (DH-485; DH+; DF1; etc.) and the baud rates, etc. ... once you get used to it, the whole process takes only a few seconds ... it’s sort of like “adding” a printer to your computer system ...

And harryting, what is a straight through cable + null modem adaptor?

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a straight through cable is pin 2 to 2 ... pin 3 to 3 ... pin 5 to 5 ... etc. ... a null modem adaptor is a small box (looks like a gender changer) that “crosses” the transmit and receive pins ... so that pin 2 goes to 3 ... pin 3 goes to 2 ... but pin 5 (signal common) still goes to 5 ...

Its a good thing there are smart people on this forumn!

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amen ... I learn something new from these guys every day ...

I hate to muddy the waters, but have you considered an Automation Direct DL06? The PLC cost is $200-$250, software and cables are less than $200... All told you can get what you need, brand new, for less than $500 and still have plenty of room to expand in the future.

Just a thought