The Siemens S7-1200 PLC uses both digital and analog inputs and outputs to communicate with field devices like sensors, switches, and actuators. In simple terms, the digital inputs receive signals such as ON or OFF (0V or 24V), representing binary states — for example, whether a sensor is detecting an object or not. The digital outputs send control signals to operate loads like lamps, solenoid valves, or contactors. Depending on the CPU type, these outputs can be relay or transistor-based, making them suitable for both AC and DC loads. Each input or output channel has a dedicated terminal, and wiring follows the standard 24V DC power supply connection. Configuration and signal mapping are done through the Siemens TIA Portal software, where users can assign addresses, set filters, and monitor signal states in real time.
Along with digital I/O, the S7-1200 PLC also supports analog inputs and outputs for applications that require variable data, like temperature, pressure, or speed. Analog inputs convert continuous real-world signals (like 4–20mA or 0–10V) into digital values that the CPU can process. Analog outputs do the reverse — they send proportional signals to devices like control valves or drives. The flexibility of the Siemens S7-1200 PLC lies in its modular design, which allows you to expand I/O points easily using extra modules. A common example is the Siemens 6ES7223-1BH32-0XB0, which adds more digital inputs and outputs to the base unit. This setup helps automation engineers build scalable systems — starting small and expanding as project needs grow. In short, the S7-1200 PLC inputs and outputs act as the bridge between your control logic and the real-world equipment, ensuring precise and reliable automation.