How do i get an existing PLC code from the system which has no software?


Thread Starter


Hi all,

The company i work for has a couple of PLC units. The had some other company come in about 8 years ago and got the code installed onto the PLC. Unfortunately we do not have the actual program code nor does the company which actually did this for us exist now.

The two PLC units are the following
1. Allen-Bradley 1746 with SLC 5/03 processor with a PANELMETER Power Pro.

2. Allen-Bradley CompactLogix L35E with a PANELVIEW PLUS 2711P-RPI

Both are individually controlled with two separate laptops. We are looking to extract the existing PLC ladder logic code to make some corrections in both the system & the HMI associated with it.

How should i be proceeding with this problem? I kinda know that RSLogix 500 is the way to go but where can i find the procedure to carry it out?

Any help will be much appreciated!

Sastry Musti

Hi Yogi,

Do the following activities.

1. Go to the PLC & check whether it has a 9 PIN D connector for communication (Serial)... I am sure, it should have. Now, go to your lab & prepare a 9 pin null modem cable for communication. The pin outs are:

2-->3, 3-->2, 5-->5 on both the ends. Make sure that you have right kind of 9 pin connectors (Male / Female)...

The communication cable is ready.

2. Now, go to Allen-Bradley site & download RS - Linx, RS Logix 500 trial version. Probably you would be able to do that. Previously i was able to do that. Now, i have the licensed copies.

After you download & install the software, connect the cable to the PLC & laptop (first to the PLC, then to the laptop) & set the commn parameters in RS linx. How to do this? I have a procedure to follow with snapshots. If you give me the personal mail ID, i will send you the procedure.

3. After communicating the PLC to laptop successfully, you can upload, modify & download the logic again to the PLC.

Your job is done.

If you don't want to the above steps, there is another simple & alternate way of doing this...

4. Call the Allen Bradley support to your plant & get it done in a professional way. Your job is done.

Best regards
Sastry Musti

bob peterson

Not a bad plan except that the free version of RSLogix 500 does not work with the SLC processor he has, and does not work at all with compact logix which is the other processor he has.

He will need to either buy the software or rent someone who has it to come in and upload it, unless whoever wrote it protected it in some way, in which case he is just out of luck (more or less).


bob peterson

I hit the send button to fast.

I don't know wat a panel meter power pro is so i won't comment on if it is possible to upload the configuration from that unit, or even what software would be needed to do so if it is even possible.

The Panelview plus unit is of a vintage where he may not be able to upload the configuration in a way that would make it possible to make any changes. The runtime file can be uploaded, but I don't know if that would do him any good. In any case, he will ened RSView studio for ME to do this.