You walk into a panel with an Allen-Bradley Micro850 2080-LC50-48QBB and a Siemens S7-1200 CPU 1214C side by side. Both are “micro” programmable logic controllers. Both run IEC 61131-3 programs. The datasheets say one does 10K program steps, the other 100 KB of work memory. But the engineers on site will tell you: the difference isn’t the memory number — it’s how that memory behaves when the machine hits its limit. This head-to-head teardown unpacks three dimensions that datasheets intentionally or inadvertently hide, using only manufacturer-published facts.
| Specification | Siemens S7-1200 CPU 1214C | Allen-Bradley Micro850 2080-LC50-48QBB | Notes |
|---|---|---|---|
| Work memory / program steps | 100 KB integrated work memory | Up to 10K program steps + 20 KB program data (1 step = 12 bytes; ~120 KB logical) | Equivalent in bytes? Roughly ~120 KB for A-B, but Siemens architecture is more memory-efficient for complex functions. |
| On-board I/O | 14 DI / 10 DO / 2 AI | 28 DI / 20 DO | A-B has more discrete I/O on CPU; Siemens has built-in analog. |
| Bit execution speed | ~85 ns (standard); 40 ns (G2) | Not published; assumed ~1–2 µs (industry estimate for similar micro PLCs) | Illustrative: Siemens is about 12-24× faster per bit instruction. |
| Integrated communication | PROFINET (programming, HMI, PLC-PLC) | EtherNet/IP + Modbus TCP + RS232/485 + USB | Both support open Ethernet protocols; PROFINET vs EtherNet/IP is a protocol difference, not a performance difference (both ~100 Mbps). |
| Motion capability | Integrated PTO (2 or 4 axes, depending on firmware) + high-speed counters | 3 PTO outputs, 6 HSC inputs | Comparable; both support up to ~200 kHz pulse trains. |
| Programming environment | TIA Portal | Connected Components Workbench (CCW) | Both IEC 61131-3; TIA Portal is more integrated but heavier; CCW is lighter but less robust. |
Number: Siemens S7-1200 CPU 1214C has 100 KB integrated work memory. Allen-Bradley Micro850 offers up to 10K program steps + 20 KB program data (1 step = 12 bytes, so roughly 120 KB logical). The raw numbers look similar — about 100–120 KB. But the mechanism differs fundamentally. Siemens PLC uses a single, contiguous work memory pool for program code, data blocks, and system blocks. Allen-Bradley PLC’s Micro850 partitions memory into program steps (code) and a separate 20 KB data area. In practice, this means: if your application needs a large data array (e.g., a FIFO buffer for 500 temperature readings), the Micro850’s 20 KB data limit forces you into convoluted workarounds — using indirect addressing to external SD card, or compressing data at the cost of scan time. The Siemens S7-1200 can allocate from the 100 KB pool flexibly; a 40 KB array leaves 60 KB for code, no gymnastics needed.
Worked consequence: In a real-world recipe-management system holding 400 product records (each ~80 bytes = 32 KB total), the Micro850 hits the data wall. Scan time creeps up 15–20% because you must page data from SD card (if you even have one; the base Micro850 lacks an SD slot). The S7-1200 holds the same array in work memory, scan time unaffected. Decision: if your machine needs >20 KB of mutable data tables, the Siemens architecture saves you from a memory-induced redesign.
When it reverses: If your application is purely logic-heavy with short data (e.g., safety interlocks, simple sequencing), the Micro850’s 10K program steps are comfortable. Also, if you already standardize on SD-card data logging and accept the slower paging, the raw step count is adequate. But for data-intensive batch control, the Siemens advantage is structural.
Number: Siemens S7-1200 CPU 1214C executes a bit instruction in ~85 ns (standard) or 40 ns on G2. Allen-Bradley does not publish bit instruction speed for the Micro850; typical values for similar micro PLCs (e.g., Omron NX1P2 primary task cycle ~4 ms, Schneider M241 response ~50 µs) suggest a micro PLC bit instruction takes on the order of 1–2 µs. But the mechanism that matters isn’t the raw ns — it’s scan cycle consistency. The S7-1200’s PROFINET interface is hard-wired into the internal bus; cyclic I/O update is deterministic, regardless of load. The Micro850’s EtherNet/IP uses a software stack that shares CPU cycles with your logic. Under high program step count, I/O jitter increases.
Worked consequence: Consider a packaging machine with 200 digital inputs and 80 outputs, program steps ~8000. The S7-1200 will complete a scan in about 2–3 ms, with I/O update within 1 ms of the scan start. The Micro850 under the same load may show a scan of 8–12 ms, with I/O jitter up to 3 ms. For a high-speed pick-and-place (cycle time
When it reverses: If your process is slow (e.g., HVAC damper control, conveyor sorting > 1 second cycle), the Micro850’s jitter is irrelevant. Also, if you invest in a CompactLogix 5380 (which has a dedicated communication processor and 1 Gbps EtherNet/IP), scan jitter drops dramatically — but that costs 4× the Micro850. For slow, cost-sensitive machines, the Micro850’s lower upfront price (roughly $350 vs. $550 for S7-1200 CPU 1214C) wins.
Number: The Micro850 2080-LC50-48QBB has 28 DI / 20 DO; the S7-1200 CPU 1214C has 14 DI / 10 DO / 2 AI. On paper, the Allen-Bradley offers 48 discrete points vs. 24. But the mechanism to watch is expansion bus speed and topology. The Micro850 supports up to 4 local I/O modules on a serial backplane. The S7-1200 expands via PROFINET (or signal modules on the internal bus) — you can add up to 8 signal modules directly on the CPU rail, plus remote PROFINET I/O with dozens of modules. The practical limit: the Micro850’s local backplane bandwidth is about 1–2 Mbps; beyond 4 modules, the scan cycle for expansion I/O becomes the bottleneck. The S7-1200’s PROFINET handles up to 100 Mbps, and each signal module adds ~10 µs of latency — negligible.
Worked consequence: A semi-automated assembly station with 60 inputs and 48 outputs. You buy the Micro850 thinking “48 points cover it,” but you need 12 more input modules. That forces an expansion chassis with 2 modules — and your scan time jumps from 6 ms to 18 ms because the backplane is shared with the CPU logic. With the S7-1200, you add two PROFINET I/O blocks (e.g., ET200SP) at 100 Mbps; scan time increases by 0.5 ms. The decision: if you anticipate future I/O growth beyond 64 points, the Siemens platform scales without scan penalty.
When it reverses: If your machine is fixed (no expansion planned) and you need exactly 48 points, the Micro850’s built-in I/O saves you two signal modules ($120 each) and the programming overhead of a remote rack. For standalone, non-growing applications, the A-B bundle wins on total installed cost.
Datasheets never mention integration pain. Siemens TIA Portal offers a single project for PLC, HMI, drive, and safety. Allen-Bradley’s Connected Components Workbench (CCW) supports only Micro800 series and PanelView 800 — if you later upgrade to CompactLogix, you must migrate to Studio 5000, a different ecosystem (and a $4,000+/year license). The datasheet says “IEC 61131-3” for both, but the cost of switching platforms mid-lifecycle is never in the spec sheet. For a machine builder who sells 50 units per year and expects a 7-year product life, the total cost of ownership includes re-engineering if the end user demands a different PLC family. Siemens TIA Portal scales from S7-1200 to S7-1500 with minimal rework; Allen-Bradley’s Micro800 to CompactLogix migration is a full rewrite.
Both PLCs can be used in safety applications, but the CompactLogix 5380 safety variant (GuardLogix) supports SIL 3 / PLe. The S7-1200 does not have a safety-rated variant in the standard CPU line; you need the S7-1200F (fail-safe) for SIL 2/3, which requires separate safety modules. If an engineer picks the S7-1200 for its 40 ns speed and then tries to integrate a safety relay externally, the scan time mismatch can cause unintended delays in the safety chain. Rule: never let scan speed drive the selection if you need integrated safety — check the safety-rated family explicitly. The Micro850 also lacks a safety-rated CPU; for safety, you must step to GuardLogix. The datasheet hides this because it lists “motion” and “security” but not the safety architecture.
If your application has any two of: (a) >20 KB of mutable data tables, (b) I/O expansion beyond 64 points, (c) cycle time 1 s), the Allen-Bradley Micro850 offers the lowest upfront cost with adequate performance. For safety-critical applications, do not use either standard CPU — step to the dedicated safety variant (S7-1200F or GuardLogix) and budget 2–3× the CPU cost.
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.