Choosing SCADA software when the PLCs are older than the PC

I can't remember the last time somebody called me because they wanted new SCADA software. They call because the SCADA PC died over the weekend, the backup turned out to be an image nobody can restore, and the license lived on a USB key plugged into that same dead box. Out on the floor, meanwhile, the PLCs are fine. Most of them have been fine for twenty years.

That's the part worth planning around. SCADA software tends to get replaced every ten or fifteen years. The controllers under it stay until they physically quit. So you pick the new package by the hardware it has to talk to, not by how good the demo screens look. Here is the order I work in: the controller list, the driver question, what the license actually meters, and a cutover that doesn't cost you a shift.

What actually retires an old SCADA software install

Hardly ever missing features. It's usually one of these, and often two at once.

The vendor walked away. NI Lookout is the cleanest example I know of. The last release, 6.7.1, came out in July 2013, and its list of supported operating systems stops at Windows 8 and Server 2008 R2. You can still download it from NI. Buying a new license is another matter, so if your plan depends on one more seat, ask NI before you count on it. AutomationDirect sold its own tailored version, LookoutDirect, a 500 I/O package that ran off a USB hardware key. It sits in their retired products now, with no replacement named.

Then there's the license, married to a PC that's about to die. Hardware keys and node-locked activations don't care how good your backups are.

Windows moves on without it. A package whose OS list ends at Windows 8 is on borrowed time the day IT pushes the next security policy to that machine.

Or the name changed and nobody noticed. There are still plenty of Wonderware and Citect systems running, and the support, upgrades and migration tools for them all sit under AVEVA names now. Worth knowing before you spend an afternoon searching for a product that technically doesn't exist anymore.

Name on the old system	What to look for today	Notes
Wonderware System Platform	AVEVA System Platform	Same object and template based product line under the AVEVA name
Wonderware InTouch	AVEVA InTouch HMI	AVEVA also offers an InTouch conversion service
Citect SCADA, Vijeo Citect	AVEVA Plant SCADA	Schneider Electric sells it under the AVEVA name as well; there is a separate Citect historian conversion
GE iFIX, Proficy iFIX	GE Vernova Proficy iFIX	Same product line, still getting new releases
NI Lookout, LookoutDirect	No successor	Last release 6.7.1, July 2013

Old SCADA software names and what they are sold as today.

Start the SCADA software search with the controller list

Before anybody opens a demo, walk the plant and write down every controller the new system will read or write. From the nameplate, not the drawing. On most of the sites I get called to, the drawings are two retrofits behind.

Four columns per controller: catalog number, firmware revision, the port and protocol it actually talks on, and whatever sits between it and the network today. That last column gets skipped more often than the other three put together. It's also where the surprises are.

On the floor	Talks	The new SCADA needs	Watch for
ControlLogix, CompactLogix	EtherNet/IP, tag based	Native Logix driver with tag browse	Every client and OPC server takes connections on the Ethernet module. A 1756-ENBT is rated for 64 TCP and 128 CIP connections, a 1756-EN2T for 128 and 256
SLC 5/05, MicroLogix 1100 and 1400	Ethernet on the built-in port, data table addresses	Driver for SLC style addressing (N7:0, B3:0)	Symbols live in the programming file, not in the processor, so the SCADA sees N7:0, not a tag name
SLC 5/03 and 5/04, MicroLogix 1000, 1200, 1500, PLC-5	DF1 serial or DH+	A gateway: 1761-NET-ENI on DF1, a 1756-DHRIO or a standalone DH+ gateway on DH+	The NET-ENI has 6 TCP connections in total: 2 incoming, 2 outgoing, 2 either way
Siemens S7-300, 400, 1200, 1500	S7 protocol over Ethernet	Native S7 driver	On a 1200 or 1500 a classic S7 driver needs PUT/GET permitted and optimized block access switched off. That is a program change and a download
OEM skids, DirectLOGIC, drives, power meters	Modbus RTU or Modbus TCP	Generic Modbus driver and a register map from whoever built it	Register offset (40001 or 0) and how the driver writes coils

The controller inventory to finish before any SCADA software demo.

Say the plant has three lines. Line 1 runs a ControlLogix with a 1756-EN2T. Lines 2 and 3 are SLC 5/04s on DH+, and years ago somebody put a 1756-DHRIO in slot 3 of the Line 1 chassis to bridge them. The wastewater skid came with its own controller and a Modbus TCP register list. Packaging is a MicroLogix 1500 with a NET-ENI on channel 0.

Five controllers. Four separate connection problems. Line 1 is the easy one, any serious package has a native Logix driver. Lines 2 and 3 route through the ControlLogix chassis: in through the EN2T, across the backplane, out of the DHRIO onto DH+. In Ignition, for example, that path reads 1,3,2,21. Backplane, the DHRIO in slot 3, DH+ channel A, station 21. The skid needs its register map checked against the actual controller, not against the manual in the OEM binder. And the MicroLogix is fine right up until the old SCADA, the new one, the HMI and somebody's laptop all want in at the same time. Which is exactly what a cutover looks like.

No ControlLogix chassis on site for a DHRIO to live in? A standalone EtherNet/IP to DH+ gateway does the same bridging job. Make sure the SCADA driver lists it as a supported path before you buy one.

The three-line example: one SCADA software server, four different ways to reach the controllers.

Native driver, generic Modbus, or an OPC server in the middle

Every controller on that list gets reached one of three ways. They don't cost the same in engineering hours.

Native driver

This is the controller's own protocol. On a Logix processor it means browsing tags by name straight out of the controller, with the data types already right. When a feature page says "supports Allen-Bradley," ask which families. Logix tags, SLC and PLC-5 data table addressing, and routing onto DH+ are three different jobs, and a package can do the first one well and the other two not at all.

Generic Modbus

Reaches nearly anything. Does nothing for you. You build the map by hand, register by register, and two things bite. First the offset: 40001 on one side, 0 on the other, and every value lands one register off. Then the coils. Function code 05 writes one coil, function code 15 writes several, and some drivers send a single-bit write as a 15 that covers a whole byte. On a controller that addresses bits one at a time, you switch off one coil and seven of its neighbors go off with it. So on any new driver I put a Modbus sniffer on the wire for the first coil write, before it gets anywhere near a pump.

OPC server in between

Kepware, or the Industrial Gateway Server that GE Vernova bundles with iFIX, buys you drivers the SCADA package doesn't have natively. It's also one more box to license and back up. Still the right answer sometimes, especially when the old system already runs through one and the tag names live there. One catch: if that old server is classic OPC over DCOM, the new package has to speak it. Ignition sells a separate OPC COM module just for that, $885 as of September 2026.

What each SCADA software license actually counts

Price talk goes nowhere until you know what the license meters. Servers, displays, clients, tags, I/O points: every vendor picked something different, and the cheapest quote on day one is not always the cheapest after the second expansion.

Package	The license counts	Check before you buy
Ignition	Servers: one license per server, unlimited tags and devices	Clients are unlimited with the Unlimited version of Vision or Perspective; session-limited versions cost less. Perpetual license. Support is 16, 20 or 24% of retail per year, and a major upgrade without it costs 65% of current retail
FactoryTalk View SE	Displays and clients	Since the 2022 licensing change every server bundle includes unlimited displays. Small, Medium and Large bundles come with 5, 10 and 25 clients. Station Lite stops at 25 displays
WinCC Unified PC Runtime	PowerTags	The number in the license name (150, 500, 1k and up) is the PowerTag count. Engineered in TIA Portal
Proficy iFIX	I/O points, per node	Point tiers have run from 75 up to unlimited, and each node is licensed as development, runtime or read-only. Newer Proficy bundles also come as subscriptions
AVEVA System Platform	Marketed as unlimited I/O and clients	Quote only, with a Flex subscription option

What each SCADA software package meters. Tiers and list prices move, so get every number on a dated quote.

Two numbers from that table I'd actually put in a budget. Ignition's Vision module with unlimited clients listed at $8,330 in September 2026, Perspective unlimited at $11,225. And that 65% upgrade charge. Skip the cheapest support plan for three years to save 48% of the license, and the first major version jump takes all of it back plus some.

Whatever the meter is, count it off your controller list, not off the old license. The old license covers what the plant had the year it was bought. Then add room. I size about a quarter over what I count, because the first thing operators ask for after go-live is more points.

Check the end of life before the license runs out

Every package in that table will be somebody's old system eventually. Three questions before you sign, and the same three for whatever you're replacing:

1.    When was the last release, and which operating systems does it list? An OS list that tops out at a Windows version Microsoft dropped years ago tells you the whole story.

2.    How does the license move when the PC dies? Ignition lets you unactivate a key and activate it on another server as many times as you want. A hardware key moves nowhere if it's the part that failed.

3.    Where does the history live, and how does it come out? Lookout, for instance, logs its history to Citadel and its alarms to a SQL Server 2008 R2 Express instance. Getting years of trends out of that is a job for before the box dies, not after.

 

If the plan leans on a free edition, read the terms for the exact version you're installing. A free tier is a policy, not a right, and policies change between versions.

Running old and new SCADA software side by side

The cutover I trust is a boring one. Both systems run at once for a while, and only one of them is allowed to write.

1.    Export the old tag list first: addresses, scaling, alarm limits, descriptions. On most sites it's the only complete description of the plant's I/O in existence.

2.    Build the new connections against the same controllers, read-only.

3.    Run both and compare values and alarms side by side every shift. Two weeks minimum on a plant that runs around the clock, longer if some equipment only cycles once a month.

4.    Watch the communication hardware. Two systems polling one PLC is double the traffic. A NET-ENI only accepts four connections from outside. Between the two SCADA systems, the HMI and a laptop running RSLinx, every one of them is spoken for.

5.    Move writes over one area at a time, and switch them off in the old system in the same step.

6.    Pull the history out before the old box goes anywhere.

 

The one that burns people is both systems writing the same setpoint. Each one "corrects" the other, the value flips between two numbers, and nobody on the floor can tell you why the pump keeps changing speed.

Parallel run: the new SCADA software reads everything from day one, and each area's writes move over only when the old system stops sending them.

The controllers stay, so plan for them staying

New SCADA software gets built around the controllers it found on day one: their IP addresses, the DH+ station numbers, the path through the DHRIO, the register map on the skid. When one of those fails, a like-for-like replacement drops back into that picture and the SCADA side never notices. A different model means new addressing and new driver settings, and every screen that pointed at it gets retested.

So the spares list for a SCADA job is really a comm hardware list. The Ethernet bridge, the DH+ module, the ENI, the processor. And the oldest parts on it are the ones Rockwell stopped making a while ago: the 1756-ENBT and the 1761-NET-ENI are both discontinued.

The 1761-NET-ENI: DF1 serial on one side, EtherNet/IP on the other, and six TCP connections to share between everything that wants in.

FAQ

How much does SCADA software cost?

Depends almost entirely on what the license counts. Ignition's price list is public, and the unlimited-client Vision module alone runs past eight thousand dollars. FactoryTalk View SE, WinCC, iFIX and AVEVA go through quotes. Budget yearly support on top, 16 to 24% of the license on Ignition's plans. In my experience the engineering costs more than any of it, mostly rebuilding screens and checking every address against the real controller.

Can new SCADA software talk to an SLC 500 or a PLC-5?

Yes, if the driver covers it and the network reaches it. An SLC 5/05 or a MicroLogix 1100 or 1400 connects over its own Ethernet port. Serial processors go through a 1761-NET-ENI, and DH+ goes through a 1756-DHRIO in a ControlLogix chassis or a standalone DH+ gateway. Either way you end up typing N7:0 style addresses on the SCADA side, because there are no tag names in the processor to browse.

Do I have to replace the PLCs when I replace the SCADA software?

No. And I wouldn't do both in the same outage. Change two layers at once and when something doesn't work, you can't tell which one broke it. Put the new SCADA in against the controllers you already have, run it a while, and deal with the controllers later on their own schedule. Keep spares for them in the meantime.

Is there free SCADA software to test with?

For proving drivers, yes. Ignition's trial runs two hours at a time and resets as often as you like. The iFIX trial comes with a renewable two-hour runtime too. That's enough to connect to every controller type on your list, on the bench or read-only on the live network, before anyone signs a purchase order. Which is the best use of a trial anyway.

Spares for the hardware your SCADA software depends on

The SCADA software is the part you get to choose. The hardware under it is the part you're stuck keeping alive. We keep the pieces that sit between the two on the shelf: 1756-EN2T and 1756-ENBT Ethernet bridges, the 1756-DHRIO and the standalone ProSoft AN-X4-AB-DHRIO for DH+, the 1761-NET-ENI for serial MicroLogix and SLC processors, and the processors themselves, from the 1747-L552 and 1747-L553 SLC 5/05 to the 1766-L32BXB MicroLogix 1400. Putting a new system in and want a spare of everything it depends on? Send the controller list and we'll tell you what's here.