but in the latest Psoc Creator there is an example project "CapSense with Tuner" for the 4000-family which uses an EZI2C-module?
EZI2C is just a varient of I2C, maybe I still do not understand
If you are using Tuner GUI, data transfer would be through I2C (in pioneer kit, USB-->I2C).
The EZI2C Slave is a unique implementation of an I2C in that all communication between the master and slave is handled in the ISR (Interrupt Service Routine) and requires no interaction with the main program flow. The interface appears as shared memory between the master and slave. Once the EZI2C_Start() function is executed, there is little need to interact with the API.
Hence EZI2C slave component is used when tuner is enabled.