ATMEL Atmel USB micro controller AT90USB647 handbook (1)

This product is a high performance, low power AVR® 8-bit microcontroller. It has an advanced RISC architecture, including 135 powerful instructions, most single clock cycle execution, 32 x 8 general purpose working registers, fully static operation, up to 16 MIPS throughput at 16 MHz, and an on-chip 2-cycle multiplier.