Modules include what kinds of

 plc module should include IO modules (analog and digital input and output modules), cpu module, communications module, the general PLC does not require power modules, such as S7-200, while others require a power supply module PLC, such as S7-300 . According to the actual needs of the PLC module combination, such as CPU + DIC) + AI (analog input) + DO (digital output) + AO (analog output) + CP (communication module), if necessary, together with the PS (power supply module) basically able to achieve the desired purpose.