More recent versions of the CY4640 (starting in version 1.1) include options to use the various co-processor interfaces. This includes the HSS interface. This kit enables the download of the firmware image over the co-processor interface to eliminate the EEPROM and and implements a protocol to communicate between an external MCU and the internal CY16. The basic theory behind this design is to place the EZ-Host into co-processor mode with the HSS enabled. EZ-Host is then under HSS control so after power on when initialization is complete, EZ-Host will wait for the external device to communicate with it. One of the first things the external processor will do is to download the stand-alone firmware image over the co-processor interface (other KnowledgeBase articles discuss downloading of firmware over the co-processor interface). Once the download is complete the external processor tells the firmware to run and a handshake mechanism is in place to send commands and data between the external MCU and the internal CY16 processor.