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Migration·7 min read·

SLC 500 to CompactLogix: the smaller migration nobody plans for

Less famous than the PLC-5 route and more common, with its own set of things that do not carry across.

Short answer

The path mirrors PLC-5 migration but at smaller scale: convert with the Studio 5000 tool, then fix addressing by hand. SLC 500 used file-based addressing such as B3:0/1 and N7:0, which converts to tags with mechanical names. Expect to rename everything, and expect analog scaling to need rechecking because the raw ranges differ between card families.

What converts, and what doesn'tBit logic96%Timers & counters82%Maths78%Addressing40%Block transfers8%PID tuning5%Roughly what an automated PLC-5 → ControlLogix pass gets through untouched

The PLC-5 migration gets written about. The SLC 500 one happens more often, usually because a card failed and there is no spare.

What is the same

The conversion tool, the addressing problem, and the verification burden. Everything in the PLC-5 article applies at smaller scale.

What is different

SLC programs are usually smaller, which means rewriting is far more often the right answer. A two thousand rung program with meaningful tag names is a week of work and leaves you with something maintainable.

Analog is the sharpest edge. SLC analog cards and their CompactLogix equivalents do not share raw ranges, so scaling constants that carry across produce readings that look reasonable and are wrong by a fixed offset.

Recheck every analog point against the new card's own documentation. Do not trust a converted scaling block.

The opportunity

These migrations are usually the first time in twenty years anybody has looked at the logic. Budget a little time to delete what is dead. There is always something switched off in 2009 that nobody removed.

Common questions

Is SLC 500 still supported?
It reached end of life and is no longer manufactured, though spares remain available through third parties. The practical driver for migration is usually a failure with no replacement part rather than a feature need, which is why these projects tend to be urgent rather than planned.
Do SLC 500 analog scaling values carry over?
Not reliably. Raw count ranges differ between SLC analog cards and their CompactLogix equivalents, so scaling constants copied across produce readings that are plausible and wrong. Recheck every analog point against the new card's documentation.

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