You’re not buying a part number. You’re buying a ratio of throughput per watt, per dollar, per hour of engineering. The datasheet says 85 ns vs 10K steps, but that doesn’t tell you whether the machine will stall or the cabinet will cook. Let’s tear down the Siemens SIMATIC S7-1200 (CPU 1214C) and the Allen-Bradley Micro850 (2080-LC50) on the dimensions that actually decide the build — instruction throughput per watt, memory proportion vs. I/O count, and the hidden cost of scanning a larger network.
Number: The Siemens S7-1200 CPU 1214C executes a bit instruction in roughly 85 ns (standard; 40 ns on G2). The Allen-Bradley Micro850 does not publish a bit-time figure; its program memory is 10K steps, each step ~12 bytes. At about 120 KB of total ladder logic space, a typical scan of 5K steps at an illustrative ~0.5 µs per step yields a scan cycle on the order of 2.5 ms.
Mechanism: These are not apples-to-apples because the architectures differ in how they batch I/O. The Siemens PLC uses PROFINET IRT to move I/O data in a separate cycle — the CPU does not wait for the bus. The Micro850 uses EtherNet/IP (standard TCP/UDP), where a 10/100 Mbps bus adds ~0.3–0.8 ms of jitter per packet depending on node count. That means the effective cycle time = scan time + bus latency, and the bus latency is a proportionally larger fraction when the scan is fast.
Worked consequence: Suppose you have a 2 ms application deadline (e.g., a cut-to-length shear). With Siemens, the 85 ns logic leaves ~1.91 ms margin for PROFINET and I/O settling. With the Micro850, the 2.5 ms scan already exceeds the deadline before any network delay — so you must either reduce step count to ~4K steps or accept a degraded cycle. In practice, a 20% reduction in program size may require re-architecting state machines (roughly 6–10 hours of CCW rework, at $85/hr = $510–850).
When it flips: If your application is a slow process — say a conveyor interlock scanning at 100 ms — then both PLCs have enormous headroom. The Micro850’s advantage is lower cost per I/O point (roughly $12–14 per onboard point vs. $18–20 for Siemens on the 1214C). The proportion flips: the instruction-speed difference becomes noise, and the total cost of I/O expansion dominates.
Number: The S7-1200 CPU 1214C has 100 KB of integrated work memory. The Micro850 2080-LC50 has 10K program steps (each 12 bytes = 120 KB) plus 20 KB of program data, for a total program memory of ~140 KB. But the Siemens work memory is execution memory; the Micro850’s is storage — the controller copies from flash to RAM on boot, but the usable runtime space is the same 140 KB.
Mechanism: The key dimension is the ratio of memory to I/O. The 1214C offers 14 DI / 10 DO onboard, expandable via signal modules to ~284 digital I/O. The Micro850 on the 48QBB variant has 28 DI / 20 DO, expandable with up to 4 local modules to roughly 100–140 points. That gives a memory-to-I/O ratio of ~0.7 KB per I/O point for Siemens, and ~1.0 KB per point for Allen-Bradley PLC — on paper, the Micro850 seems more memory-rich.
Worked consequence: But that’s misleading because the Siemens work memory holds code plus data plus system blocks. A PID loop with 8 analog inputs and 4 outputs consumes roughly 12 KB of data blocks on TIA Portal. After adding 50 KB for a typical machine program, plus 20 KB for system diagnostics, you have ~18 KB left — tight for an extra axis or recipe array. On the Micro850, the 140 KB is purely program + fixed data; dynamic variables live in the 20 KB data area, so adding 10 recipes of 1 KB each consumes half that space. The proportion of memory that is usable for expansion is roughly 18% of total for Siemens vs. 14% for Micro850 when you account for system overhead — they are closer than the raw numbers suggest.
When it flips: If you are building a data-heavy application — recipe management with 50+ variants, or a historian buffer — the Micro850’s 20 KB data area becomes a wall. You hit it after roughly 12–15 recipes (assuming 1.2 KB per recipe). The Siemens, despite a smaller work memory, uses data blocks that can be paged via the memory card (up to 2 GB SD card). So the real constraint is not total memory but data access speed: if you need sub-ms access to large tables, the Micro850’s internal 20 KB is faster but smaller; if you can tolerate 10–20 ms access to SD, the Siemens wins on capacity. For machine builders who sell variants, the Siemens allows one code base with external data sets; the Micro850 forces a firmware rebuild for each variant.
Number: The S7-1200 supports an illustrative 16–32 PROFINET devices (depending on IO controller load). The Micro850 handles up to 4 local I/O modules plus Ethernet/IP nodes — typical applications stay at 8–12 total nodes. The CompactLogix 5380, a much larger platform, supports up to 180 Ethernet/IP nodes; but the Micro850 is not a 5380.
Mechanism: The relevant proportion is bus utilization. PROFINET RT (cycle time 1–4 ms) sends I/O data in a deterministic, scheduled time slot. EtherNet/IP uses standard UDP with no scheduling; each node adds a cumulative polling delay. At 10 nodes with 50 bytes of input each, the Micro850’s 10/100 port takes roughly 0.4 ms to poll all (ignoring collisions). That is 16% of a 2.5 ms scan — meaning the bus adds 16% jitter. On the Siemens, the PROFINET cycle is synchronized to the CPU cycle, so the bus does not add jitter; it just adds a fixed offset.
Worked consequence: For a packaging machine with 12 smart sensors and 3 variable-frequency drives, the Siemens can run a 4 ms application cycle with no cumulative jitter. The Micro850, under the same load, would see a scan-to-scan variation of roughly 0.5–0.8 ms (bus jitter + scan jitter), which can cause periodic missed windows for registration marks or torque limits. The practical result: you must either (a) oversize the machine timing — adding 10% to cycle time and losing throughput — or (b) add a separate real-time bus gateway, which increases cost by $600–900.
When it flips: If your network has 4 nodes or fewer (a simple conveyor with one VFD and two sensor clusters), the Micro850’s EtherNet/IP jitter is negligible compared to the scan time. The cost difference (Micro850 base ~$350 vs. S7-1200 ~$500) then dominates the decision. For a 10-machine line, that $1,500 saving may outweigh the 2% throughput loss.
Number: Both platforms support IEC 61131-3 (LD, FBD, SFC, ST). Siemens programs in TIA Portal (V17+); Allen-Bradley in Connected Components Workbench (CCW, v12+). TIA Portal integrates drive, HMI, and network configuration in one project; CCW requires separate tools for drives (Drive Tools) and HMI (View Designer).
Mechanism: The multiplier is debug time per change. In TIA Portal, a cross-reference search across 1200 devices takes about 2 seconds; in CCW, due to its architecture, a similar search can take 8–12 seconds for a 50-PLC network. That is a 4–6× factor. For a technician making 20 cross-reference checks per day, the cumulative delay is roughly 2–3 minutes per day — but the real cost is the interruption to thought flow.
Worked consequence: Over a 6-month project with 200 engineering hours, the TIA Portal saves an estimated 15–20 hours of waiting time. At $85/hr, that’s $1,275–1,700 — more than the hardware cost difference. Conversely, CCW’s smaller learning curve (roughly 40 hours vs. 80 hours for TIA) can reduce first-project cost by ~$3,400 for a new engineer.
When it flips: If you have an existing Rockwell code base and one experienced CCW programmer, the learning cost disappears. The decision then hinges on hardware cost per point and network determinism, not IDE speed.
| Dimension | Siemens S7-1200 (1214C) | Allen-Bradley Micro850 (2080-LC50) | What it means proportionally |
|---|---|---|---|
| Bit instruction time | 85 ns (std), 40 ns (G2) | ~0.5 µs (estimated per step) | Siemens is ~6–12× faster per instruction; the gap is irrelevant if scan time >20 ms |
| Work memory / data area | 100 KB (code + data + system) | 120 KB program + 20 KB data | Usable expansion memory similar after overhead; Micro850 data area is the bottleneck |
| On-board I/O | 14 DI / 10 DO | 28 DI / 20 DO | Micro850 gives 60% more onboard points, reducing need for expansion modules |
| Network determinism | PROFINET RT with scheduled cycle | EtherNet/IP with UDP polling | Siemens adds zero jitter; Micro850 adds ~0.4–0.8 ms at 10 nodes — a 16–32% jitter at 2.5 ms scan |
| Programming environment | TIA Portal (integrated, 80-hr learning curve) | CCW (40-hr learning curve, slower cross-references) | TIA saves 15–20 hr in debug wait per project; CCW saves $3,400 in first-project training |
One non-obvious insight: The Micro850’s 20 KB data area is not simply “smaller” — it is non-expandable. If you exceed it, there is no memory card option for runtime data; you must redesign the program to compress or offload to an HMI. That is a failure mode that typically appears after the machine is in production, when a customer requests 12 additional recipe slots. Siemens’ data block architecture, while smaller overall, allows partial paging from the SD card, so the same failure mode appears only when you exceed 100 KB of active simultaneous data — a higher threshold for the same class of problem.
Failure mode: the cheap PLC that costs more. If you spec the Micro850 on a 10-node, 3 ms cycle machine because the base price is $150 lower, you may discover in commissioning that the bus jitter causes a 4% reject rate on the registration system. Fix: add a $700 gateway or increase cycle to 4 ms (losing 25% throughput). The total cost delta becomes $850 vs. the Siemens at $500 — the cheaper PLC costs $350 more in realized cost. The proportion flips again: the decision rule is not “cheapest base price” but “cheapest total cost to meet the cycle deadline.”
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.