Question: What is the use of the EA pin with regards to the enumeration/firmware download process.
Answer: When EA=0, and the EZ-USB FX chip is powered, the 8051 is reset by the host setting the CPUCS Register to 0 (Your Loader Driver performs a Cypress download of the embedded 8051 firmware into the EZ-USB FX chip and then releases the Reset of the EZ-USB FX 8051 processor and your firmware code starts running). In this case either the VID/PID is obtained from the exteranl EEPROM if there is on, if not the device sends the default VID/PID. In either case the device is recognized by the host (assuming the VID/PID is of course valid and is bound to a specific driver) When EA=1 the EZ-USB systems use external program memory containing 8051 code and USB device descriptors, which include the VID/DID/PID Bytes. Because these systems do not require an I2C-compatible EEPROM to supply the VID/DID/PID, the USB core automatically releases 8051 reset on power up. Your firmware MUST supply the VID/PID. If not then the device will not enumerate correctly. Make sure your firmware already in the external EPROM/Flash does this.
Please see Section 5.3.2. "Memory Maps" of the TRM for further information .
