The Siemens S7-1200 PLC can support multiple modules to expand its input, output, and communication capabilities based on the CPU model used. In general, the S7-1200 can handle up to 8 signal modules (SMs) and 3 communication modules (CMs), depending on the specific CPU. For example, the CPU 1211C does not support additional signal modules, while the CPU 1212C supports up to 2 SMs. The CPU 1214C, 1215C, and 1217C can each support up to 8 signal modules, allowing more flexibility for larger automation systems. These modules are used to add digital and analog I/O points for sensors, actuators, and other field devices.
On the communication side, up to 3 communication modules can be installed on the left side of the CPU for connecting networks like PROFINET, PROFIBUS, or serial communication. In addition, one signal board (SB) or communication board (CB) can be mounted on top of the CPU for small expansions without increasing panel width. This modular design helps users customize the system as per their application size. So, depending on the model, the Siemens S7-1200 PLC can support a total of up to 12 modules, making it suitable for both small and medium automation projects that need flexibility and scalability.