ATMEL Atmel USB micro controller AT90USB162 handbook (1)(1)

ATmega16U2 is a high performance, low power AVR® 8-bit microcontroller with advanced RISC architecture, 125 powerful instructions, most of which are executed in a single clock cycle, 32 x 8 general purpose working registers, fully static operation, up to 16 MIPS throughput at 16 MHz