S7 300 tutorial introduces the basic structure of S7-300/400, the main manufacturers of PLCs, the Chinese website of Siemens Automation and Drive Group, and the working process of PLCs
This manual introduces the modular Siemens S7‑300/400 PLC family, describing the rack, CPU, power, signal, function and communication modules. It covers basic logic operations, scan cycle processing, and wiring diagrams for both digital and analog I/O.
The document also details module diagnostics, LED status indicators, and configuration options such as RS‑485, PROFIBUS‑DP and MPI interfaces, providing the information needed for installation, programming and troubleshooting. This manual is written in Chinese.
| CPU RAM size | S12KB, up to 8192 memory bits |
|---|---|
| Counter range | 1‑999 |
| Timer range | 10 ms‑9990 s |
The RUN LED (green) lights when the CPU is in RUN state.
It is the time the operating system needs to complete one scan cycle as shown in the diagram.
The CPU module has S12KB RAM, providing up to 8192 memory bits.