I recently received a message from someone who had just purchased a used machine with a SLC-500 based control system on it.

SLC-500 FamilyBecause most of his existing systems use simple relay controls, the new owner of the machine was reaching out to me about training on the SLC-500, as well as to ask several questions which all boiled down to, “Is the SLC-500 still viable?”

I believe the reason for that question was due in large part to the fact that when he tried to get support for the SLC-500, he felt the local rep was only interested in selling him an upgrade to ControlLogix.

So today’s question is, “Is the SLC-500 still viable?”

To be frank, if you’re building a new system today you should absolutely not be using the SLC-500. In fact, it’s my opinion that any system you built in the last ten years should not have been built using a SLC-500.

While many of you may think that’s an obvious statement, just a few years ago a company duped one of our local towns here in the Berkshires into buying a complete control system based on the ancient SLC-500 (ugh.)

SLC-500 SystemFor those who don’t know, the SLC-500 product line came out nearly thirty years ago, and using it on new systems would be akin to using 286 PCs along with 5.25″ floppy disks.

That’s not to say it’s a bad product, or that you should worry about your installed base of SLC-500s, but you should be aware of a few things.

First, Rockwell makes very few new SLC-500s today, and they are expected to stop making all SLC-500 products in the coming years.

This means if you do use SLC-500s in production, you’ll want to be sure you acquire (and thoroughly test if recycled) ample spares to keep your machines going for years to come.

Second, you also need to be sure you know what and where your RSLogix 500 software licenses are, and consider getting a basic Rockwell support contract to cover your SLC-500 and RSLogix 500 if they’re used on critical machines.

If you don’t currently have SLC-500s in your plant, but you’re looking to buy a used machine that has one on it, you’ll want to take the following into consideration:

Shawn teaching a SLC-500 (PLC) Class in 2005

First, you need to be sure the machine runs!

No joke, I have seen more than one company buy a machine that does not run because the PLC no longer has the correct (or any) program loaded (i.e. the battery died, there’s no EEPROM present or it was never updated, etc.)

Second, you need to make sure you’re not locked out of the program because it has a password no one knows!

To properly troubleshoot a PLC system, you need to have access to the PLC program. But if it’s locked with a password no one knows, you won’t be able to access it.

Third, while Rockwell has unfortunately doubled the price of RSLogix 500 over the last decade (it now costs nearly $2,900) if you’re budgeting to buy a used machine that uses a SLC-500, also budget for a copy RSLogix 500 and a copy of my affordable PLC Basics course which will get you started with PLCs and RSLogix.

MicroLogix-SLC-500-FiIf you don’t, you may find yourself with a machine that goes down for days at a time as you wait for your local integrator to schedule a visit.

PS – I’m curious how many of you still have SLC-500’s running in your facility?

If you do, please let me know by clicking on the comment link below!

Until next time, Peace ✌️ 

Shawn M Tierney
Technology Enthusiast & Content Creator

Have a question? Join my community of automation professionals and take part in the discussion! You'll also find my PLC, HMI, and SCADA courses at TheAutomationSchool.com.

If you found this content helpful, consider buying me a coffee here.

shawntierney avatar


The Automation Blog's SLC-500 Library

Cables and Adapters
Connecting HMIs
Learning and Discussion:


Please enter your comment!
Please enter your name here