This document introduces the basic structure and working principle of S7-300/400 modular PLC, as well as information about major manufacturers such as Siemens. S7-300/400 consists of rack, CPU module, signal module, function module, interface module, communication processor, power module, and programming device. The document also covers topics such as logical operations, working process, and scanning process of PLC.
The manual introduces the modular architecture of the S7‑300/400 PLC family, describing the rack, CPU, power, signal, function and communication modules. It also lists the major PLC manufacturers and provides links to Siemens' download portals.
Further sections detail the scan cycle, input/output image registers, wiring diagrams, LED status indicators, CPU classifications, module diagnostics, and PID controller tuning methods, giving a comprehensive overview for users and technicians. This manual is written in Chinese.
| CPU RAM | 512 KB |
|---|---|
| Memory bits | 8192 |
| Timers | 512 |
| Counters | 512 |
| Digital I/O points | 65536 |
| Analog channels | 4096 |
| Instruction count | ≈350 |
| Counter range | 1‑999 |
| Timer range | 10 ms‑9990 s |
The red SF LED lights when the CPU has a hardware fault or software error.