Urgent Requests to all Allen Bradley Experts


Thread Starter

Michael Lindstrom

To All,

As my age does not allow a great knowledge of legacy products, I have to call on the more experienced gentleman in the Automation area for help. I have a PLC 2 which no one at the mine has a cable to connect to. Does anyone know the pin-outs to connect from a standard Com port to a PLC 2. Or better still does anyone know if I can connect from my PCMK card to the PLC 2. I have a 1784-PCM5. Or is there a better way I am open to solutions, (this device is not networked so a lot of common options are out).

The obvious plan is to upgrade the processor to a control logix platform and keep the existing I/O. Any clues tips or more importantly warnings from
those out there who have successfully completed the code transfer.

The winder has not been touched since the initial commissioning, so hopefully the code they have is still O.K.

Any help would be much appreciated.


Michael Lindstrom
Control and Instrumentation Engineer
[email protected]

Walter Bennett

Hey answer to your question 1. you need to get the AB 1784-PCM2/B cable then you will have to use a dos driver that AB sell to make you 6200 PL2
programming software recognize the pcmk card in the DOS environment.

Walter Bennett
Systems Intergrator
Ph: 469-358-0882
mailto:[email protected]

Bob Peterson

1. The PLC2 port uses a 20 mAmp current loop interface. It would not hook up direct to your RS232 port without some kind of adapter/convertor.

2. AB used to sell smart cables for this purpose. You might be able to buy/borrow one from them yet today.

3. AB sold PLC2 to PLC5 conversion software that worked pretty well.

Bob Peterson
Hi Michael,

Your most straightforward method to connect to this PLC-2 is to get a 1784-PCM2 cable for your existing 1784-PCMK card. Check the Series letter of the PCMK card; the Series A and Series B card connectors are different and you'll want a cable whose Series letter matches your card.

The PCMK then will let you communicate to the PLC-2 front port with 6200-series PLC-2 software or with AI-2 software.

Upgrading to a ControlLogix? Do the conversion by hand; this is just one machine and you won't be able to justify the cost of the AI-2/AI-5 conversion automation utility (though you could hire out a one-time code conversion for a fraction of the cost of the software). There is no automated utility to directly convert from PLC-2 to ControlLogix code.

The thing you should be worried about is re-using the I/O. Though the ControlLogix will run rings around PLC-2 and PLC-5 controllers on local I/O chassis, if you give it the disadvantage of having to communicate over a RIO or ControlNet link to the I/O modules (where the PLC-2 had local backplane access) you might handicap your powerful controller. You said this is a winder application: usually those rely on quick I/O updates.

More details yield more advice. There are a few ancient modules that might not be easily supported by Logix. You haven't mentioned the I/O count or the model number of the PLC-2 you have today.

You'll also find some good advice over on PLCS.NET and MRPLC.COM.

Good luck,

Ken Roach
A-B Seattle
[email protected]



There is no direct connection possible between a PC COM port and the PLC-2 front port. That front port was designed about six years before IBM standardized the COM port we know today. During the eighties, some "smart cables" were available to do the electrical conversion, but they don't seem to be available anymore.

It is possible to connect a modern notebook computer to a PLC-2 using AI-2 software, the 1784-PCMK, and a 1784-PCM2 cable. (Make sure your PCMK and PCM2 are of the same series, preferably Series B.)

However, if you are familiar with the PLC-5 and not familiar with the PLC-2, I strongly recommend that you upgrade the 2 to a 5. The PLC-5 will be compatible with modern software and network products, and will be able to interact with ControlLogix as you bring that into your plant.

PLC-2 to PLC-5 conversion works perfectly, and requires no I/O rewiring.

Also, Allen-Bradley offers an incentive for doing it:


You will need to have someone assist you with the upgrade. Contact your RA distributor for advice on that. I sometimes do this as a courtesy for
my clients, but third parties can handle it.

I like your idea about migrating all the way to ControlLogix, and I know how I would do it, but the work and expense of that are not necessary in
your case.

If you decide to stay at the PLC-2 baseline, feel free to contact me offlist for some setup details for your particular situation.

Hope this helps!::

Larry Lawver
Rexel / Central Florida

Rocco F. Dominick

Dear Michael,

Download the "Hardware Configuration Manual Reference Guide" from Allen-Bradley / Rockwell Automation. It contains the schematics for all of AB's cables. The cables are listed by part number and not according to the PLC they interface to. Unfortunately, there is no manual part number. Hopefully you will be able to find the manual by the title.

Good Luck.

Rocco F. Dominick
Butech, Inc.
550 South Ellsworth Avenue
Salem, OH 44460
Phone: 330-332-9913 EXT:267
Fax: 330-337-0800
Web: www.butech.com
E-mail: [email protected]
These opinions are my own and are offered on the basis of Caveat Emptor.

Michel A. Levesque, eng.

You can use a 1785-PCM2 cable to talk to your PLC2.
As far as converting your application. I would change your PLC2 processor to a PLC5 instead of a ControlLogix for the following reasons:
1. You can just pull the PLC2 processor out (assuming that it is a mini-plc2) or pull the adapter card out (for a plc-2/30 and such).
2. You can easily convert a PLC2 code to a PLC5 by using AB conversion utility or by getting an integrator to do this. (conversion will
typically get 80% of the code back, the rest must be hand-coded).
3. Your maintenance personnel will adapt more easily from a PLC2 to a PLC5 code base than to a CLX code base.
4. Overall the transition is easier from PLC2 to PLC5 since to get the code to a CLX means converting PLC2 to PLC5 then converting PLC5 to
CLX (no direct conversion possible unless you want to re-write from scratch).

Bob Peterson

> PLC-2 to PLC-5 conversion works perfectly, and requires no I/O rewiring.

I would NOT describe it as perfect. There are any number of issues with the conversion process, not the least of which is that any numerical or arithmatic functions frequently do not work the same. The PLC2 used 3 digit BCD math. People often did odd things. Also, sequencers do not work the same and have to be manually converted.

The straight RLL stuff converts well (perfectly might describe it), but anything beyond that is suspect. it does do a good job of pointing out the things it does not convert. Also some things it converts end up with some really odd code and strange addresses.

Do not expect to do this in a few hours. You will need to look closely at the end result.

Bob Peterson



I have done a LOT of 2 to 5 conversions, and my experience has been excellent, thus my enthusiasm.

Yes, there are issues in math conversions, addressing, etc., but I've never taken more than a few minutes to resolve them. I'll acknowledge that this takes a high degree of skill with both the 2 and the 5, but lots of people have that, and I encouraged Michael to seek that help.

Obviously, your experience has been different, though, so I'll cheerfully take back my adverb "perfectly". Will you accept "very well"?

Larry Lawver
Rexel / Central Florida

Some time ago, longer than I care to remember, I designed a solution to the dilemma. It's an equivalent to the smart cable as it was called then (15 pin D shell to PLC-2 front port to floating interface pod with wall-wart 120VAC P/S and on to 25 pin D shell to computer RS-232) . We never marketed it since I sensed that it would strain our good relations as developers and integrators with A-B and Icom. Since it is now an antique product I don't think anyone will mind if we take offers.

On the subject of PLC upgrading, after having done quite a slew of them I recommend not using the existing program for anything. Use the I/O description (if it is any good), but design the program from scratch with the old program as a guide only. PLC-5 and especially CLX provide an opportunity to create a much better (and more understandable) solution. Just use the old program as a reference in specific areas where it's needed. Reshuffling automatically created rungs from a conversion program is more frustrating and provides no new insight - just gets you too attached to how things used to be done (without knowing why).