EZ-USB (AN2131) was originally developed by Anchor Chips. Cypress bought Anchor Chips and developed afterwards EZ-USB FX and EZ-USB FX2 (CY7C68013). All of these chips have an 8051 core and a USB interface. The main difference is that the FX2 uC has a USB 2.0 (high speed) interface and more I/O pins than the previous versions, while EZ-USB (AN2131) supports USB 1.1 and EZ-USB FX supports both USB 1.1 and USB 2.0 (but only at the full speed). Also with EZ-USB FX2 (CY7C68013) you can interface ATA devices, such as CD-ROMs, hard disks, compact flash memories, etc, easier than you would do with EZ-USB (AN2131) and EZ-USB FX. You 'll discover more of all these chips, if you download the datasheets, manuals, application notes, etc. Cypress offers even reference designs...

George