People search for 6ES7214 and stop there. It is the first block of every CPU 1214C, and the CPU 1214C comes in three variants that do not replace one another.
What the three groups mean
Siemens names each S7-1200 CPU variant by its power supply, its digital inputs and its digital outputs, in that order. DC means 24 V DC, AC means mains voltage, RLY means relay outputs. The inputs are 24 V DC on all three.
| Variant | Order number | Supply | Outputs |
|---|---|---|---|
| DC/DC/DC | 6ES7214-1AG40-0XB0 | 24 V DC | transistor, 24 V DC |
| AC/DC/RLY | 6ES7214-1BG40-0XB0 | 120/230 V AC | relay |
| DC/DC/RLY | 6ES7214-1HG40-0XB0 | 24 V DC | relay |
Everything else is the same on all three: 14 digital inputs, 10 digital outputs, 2 analog inputs and one PROFINET port. The letter after the 1 in the second block carries the variant: A, B or H. Older generations of the CPU keep that letter and change the rest of the block, so read the whole number.
Transistor or relay outputs
Transistor outputs switch fast and silently and carry up to 0.5 A each at 24 V DC. Relay outputs carry up to 2 A, switch AC or DC loads and isolate the load circuit, but they wear with every switching cycle and are too slow for pulse outputs. If the machine drives a stepper or a servo with pulse train outputs from the CPU, it needs the DC/DC/DC variant, or a signal board that adds fast outputs.
What happens if you fit the wrong one
An AC/DC/RLY CPU on a 24 V DC supply does not start. A DC/DC/DC CPU connected to mains is likely to be destroyed. Between DC/DC/DC and DC/DC/RLY the supply is the same and the failure is quieter: a relay output wired where the program expects fast pulses misses them, and an AC load on a transistor output does not switch.
The project matters too. The hardware configuration in TIA Portal names the exact order number. A different variant means changing the device in the project and downloading it again, so plan for a laptop with the right TIA Portal version and a current copy of the project.
Firmware and generations
The 40 at the end of the second block marks the current generation of the first S7-1200 series, which runs firmware version 4. A newer spare usually runs an older program once the device in the project has been changed to the new order number. A spare with older firmware than the project can refuse it until its firmware is updated. Siemens has also introduced a second generation, the S7-1200 G2, with order numbers of its own; it is not a drop-in replacement without project work.
Ordering the right spare
Read the full number off the plate, including the firmware version where the label shows it, and search for that. If the exact code is not listed, the same variant from a newer generation is usually the practical choice. The guide to Siemens order numbers explains the other blocks, and if the machine still runs an S7-300, the S7-300 to S7-1500 migration guide covers the larger decision. Search the code on Sparehawk or post a wanted request for it.