The firmware for the Touch MCU is based on the QTouch library. The QTouch library handles the touch acquisition. The touch measurement values are made available for the application firmware trough an API, which is described in detail in the QTouch Library user Guide.
The touch measurement values available trough the Touch Library API is sent to the QT600IB with a SPI Master or TWI Master serial interface, using a custom protocol. AVR QTouch Studio will read these data packets from the QT600IB. See the QT600 Protocol Document for details about the communication protocol.