https://en.wikipedia.org/wiki/Combined_Charging_System
- Basic signaling (BS) is done using a PWM signal which is transferred over the control pilot contact (CP) according to IEC 61851-1. This communication is used for safety-related functions, indicating for example if the connector is plugged in, before contacts are made live (or energized), and if both charging station and electric vehicle are ready for charging. AC charging is possible using the PWM signal only. In this case the charging station uses the duty cycle of the PWM to inform the onboard charger of the maximum available current at the charging station.
- High-level communication (HLC) is done by modulating a high-frequency signal over the CP contact (also known as Power Line Communication or PLC) to transfer more complex information, which may be used e.g. for DC charging or for other services such as "plug and charge" or load balancing. High-level communication is based on the standard DIN SPEC 70121 and the ISO/IEC 15118-series. For DC charging DIN SPEC 70121 supports only charging powers up to 80 kW; for higher powers communication according to ISO/IEC 15118 is mandatory.