The MAX3421E USB peripheral/host controller contains the digital logic and analog circuitry necessary to implement a full-speed USB peripheral or a full-/lowspeed host compliant to USB specification rev 2.0. A built-in transceiver features 15kV ESD protection and programmable USB connect and disconnect. An internal serial interface engine (SIE) handles low-level USB protocol details such as error checking and bus retries. The MAX3421E operates using a register set accessed by an SPITM interface that operates up to 26MHz. Any SPI master (microprocessor, ASIC, DSP, etc.) can add USB peripheral or host functionality using the simple 3or 4-wire SPI interface. The MAX3421E makes the vast collection of USB peripherals available to any microprocessor, ASIC, or DSP when it operates as a USB host. For point-to-point solutions, for example, a USB keyboard or mouse interfaced to an embedded system, the firmware that operates the MAX3421E can be simple since only a targeted device is supported.