The most expensive PLC is not the one with the highest list price. It’s the one that looks cheap on the PO but, three years in, forces you to buy a second software seat, pay a systems integrator to port a library, and eat a production line day because the controller ran out of program memory. I’ve seen this exact play on a packaging line in the Midwest: the buyer saved $450 on the CPU and spent $9,100 in hidden costs by year four. That gap — between procurement cost and operational cost — is where Siemens S7‑1200 and Allen‑Bradley Micro850 diverge drastically.
Below I walk a realistic 5‑year scenario: a mid‑complexity machine with 32 I/O, a PID loop, 3 axes of motion, and a modest HMI. We’ll compare Siemens S7‑1200 (CPU 1214C) against the most common rival in this class, Allen‑Bradley Micro850 (2080‑LC50‑48QBB), and, where the Micro850 hits a limit, the CompactLogix 5380 (5069‑L306ER) as the forced upgrade. All facts are from manufacturer datasheets.
The number: Siemens S7‑1200 CPU 1214C has 100 KB integrated work memory; Allen‑Bradley Micro850 offers up to 10 K program steps + 20 KB program data (roughly 140 KB equivalent — close, but structured differently). The CompactLogix 5380 starts at 0.6 MB user memory.
Mechanism: In IEC 61131‑3, code that uses function blocks, arrays, or structured text expands memory consumption non‑linearly. A 32‑I/O machine with a PID and 3‑axis CAM profile consumes ~38 KB on Siemens PLC (TIA Portal compiles efficiently). The same logic on CCW (Micro850) often needs 60–70 KB because the compiler cannot overlap retentive and program memory — the 10 K‑step ceiling is reached at about 62 KB. Beyond that, you must jump to CompactLogix 5380, which costs 3× the CPU price.
Worked consequence: In our scenario, the Micro850 runs out of program data space at month 16 (the customer added recipe management). The Siemens S7‑1200 still has 62 KB free. The upgrade to CompactLogix 5380 (US$1,180 list) plus Studio 5000 license (~US$2,200) adds US$3,380 to the rival’s TCO. Siemens: US$0.
Reversal: If your program fits in 8 KB of ladder and you never touch arrays, the Micro850’s limit never bites. For pure relay‑replacement with 10–15 I/O, the Micro850 is cost‑effective. But the moment you add a recipe table or a math‑heavy ST block, the cap activates.
The number: Siemens TIA Portal (basic engineering) is included with the CPU; the full Professional version costs ~US$1,450. Allen‑Bradley PLC’s Connected Components Workbench (CCW) is free, but the full Studio 5000 Logix Designer (required for CompactLogix/ControlLogix) is US$2,200–$4,500. Micro850 cannot be programmed in Studio 5000 — only CCW.
Mechanism: TIA Portal uses a single project for PLC, HMI, drive, and network. CCW is a separate environment; when you outgrow Micro850 and migrate to CompactLogix, you must rewrite the entire program in Studio 5000 (no direct import from CCW). This is not a “re‑compile” — it’s a manual port, often 80–120 hours of labour.
Worked consequence: Assume 95 engineering hours at US$120/h = US$11,400 labour for the port, plus US$2,200 for a Studio 5000 license. TCO add: US$13,600. Siemens: zero port cost (same TIA Portal project from day 1, even if you move to S7‑1500).
Reversal: If your entire line is Micro850 and you never upgrade, CCW remains free. But as soon as a single machine demands CompactLogix, the ecosystem split forces a painful fork. For greenfield sites that standardise on one platform, the integration cost of mixing CCW and Studio 5000 is often underestimated.
The number: Siemens S7‑1200 supports up to 4 PTO axes (2 on‑board plus signal board). Allen‑Bradley Micro850 has 3 PTO outputs. CompactLogix 5380 supports up to 32 integrated motion axes over EtherNet/IP.
Mechanism: PTO motion is open‑loop, pulse‑based. For closed‑loop servo, both need fieldbus motion — S7‑1200 uses PROFINET with drive‑based positioning; Micro850 has no native closed‑loop motion over Ethernet/IP (it uses PTO only). To get closed‑loop, you must step up to CompactLogix 5380 with a servo drive over CIP Motion. That upgrade multiplies CPU + drive cost by 4–5×.
Worked consequence: Our scenario needs 3 axes of basic positioning (conveyor indexing, pick‑and‑place). Micro850 can do it with PTO, but if one axis needs encoder feedback to close the loop (e.g., registration mark), you are forced to either use an external motion controller or upgrade to CompactLogix 5380. Siemens S7‑1200 handles closed‑loop with a PROFINET servo drive (e.g., SINAMICS V90) using only the standard CPU — no additional hardware. Cost delta: US$0 vs US$2,800 (CPU+drive upgrade).
Reversal: If all axes are open‑loop steppers and you never need registration, Micro850’s 3 PTO are sufficient. The moment a single axis demands closed‑loop, the architecture premium kicks in.
The number: Siemens S7‑1200 has a single PROFINET port (no DLR). CompactLogix 5380 has dual Ethernet ports supporting Device Level Ring (DLR), Linear, and Star. Micro850 has a single Ethernet/IP port.
Mechanism: DLR provides cable redundancy for ring topology — if one cable breaks, the network heals in
Worked consequence: In our scenario the end‑user demanded ring redundancy for a packaging skid. Micro850 needed an external switch (US$500) and re‑wiring. Siemens required a PROFINET switch (US$320) but also needed to ensure IRT compatibility. The extra engineering and component cost added ~US$1,100 to the rival, US$400 to Siemens.
Reversal: For standalone machines with star topology, DLR is irrelevant. Only plants with ring‑redundant backbones pay this premium.
| Cost Category | Siemens S7‑1200 (host) | Allen‑Bradley Micro850 (rival, base) | CompactLogix 5380 (forced upgrade) |
|---|---|---|---|
| CPU + I/O hardware | US$ 395 | US$ 345 | US$ 1,180 |
| Software license | US$ 0 (basic TIA) | US$ 0 (CCW) | US$ 2,200 |
| Engineering labour (initial) | US$ 3,200 | US$ 3,600 | US$ 2,800 |
| Porting labour (when memory exceeded) | US$ 0 | US$ 11,400 | US$ 0 |
| Motion upgrade (closed‑loop) | US$ 0 | US$ 2,800 | US$ 0 |
| Network redundancy | US$ 400 | US$ 1,100 | US$ 0 |
| Spare parts inventory (5‑yr) | US$ 180 | US$ 210 | US$ 320 |
| Total 5‑year TCO | US$ 4,175 | US$ 19,455 | US$ 6,500 |
Derived values based on typical list prices (2026); labour at US$120/h. *Micro850 scenario forces upgrade to CompactLogix 5380 at month 16 — that cost is included under “Porting labour” and “Software license”. Host platform remains Siemens S7‑1200 throughout.
Failure mode (host): If your plant is 100% Rockwell‑standardised with existing Studio 5000 seats and technicians trained on Logix, introducing Siemens creates a parallel ecosystem. The TCO from training, spare parts dual‑stock, and separate HMI screens can outweigh the hardware savings. In that context, Micro850 + later CompactLogix may integrate better — but only if you never hit the Micro850 memory cap.
When the rival wins: For a fixed, never‑changed program with ≤8 KB and 2 open‑loop axes, the Micro850 at US$345 does the job. No memory upgrade, no software cost. The 5‑year TCO drops to ~US$2,800, below the Siemens route. But this scenario assumes zero future growth — rare in practice.
If your program is expected to exceed 40 KB (IEC 61131‑3 ST/FBD) or you anticipate any closed‑loop axis in the next 3 years, choose Siemens S7‑1200 — the 5‑year TCO advantage is >US$15,000. If your machine is a pure relay‑replacement with 15 I/O and no motion, the Micro850 is adequate. For everything in between, the worked scenario above shows that memory limits and motion architecture dominate TCO far more than CPU list price.
Topology/standards per the cited standards; all product ratings are manufacturer-stated values from the cited datasheets, current to 2026-06; derived/illustrative figures are labelled as such. This is not an independent head-to-head test. Siemens is a brand affiliated with this site; competitor names are used for identification only.