Description
USS-820D is a USB device controller that provides a programmable bridge between the USB and a local microprocessor bus. It is available in two package types: 44-pin MQFP (USS-820D) and 48-pin TQFP (USS-820TD, formerly USS-825). The USS-820D allows PC peripherals to upgrade to USB connectivity without major redesign effort. It is programmable through a simple read/write register interface that is compatible with industry-standard USB microcontrollers.

Features
■ Full compliance with the Universal Serial Bus Specification Revision 1.1.
■ Backward compatible with USS-820B and USS-820C revisions.
■ Self-powered or bus-powered USB device. Meets USB power specifications for bus-powered devices.
■ Full-speed USB device (12 Mbits/s).
■ USB device controller with protocol control and administration for up to 16 USB endpoints.
■ Supports control, interrupt, bulk, and isochronous transfers for all 16 endpoints.
■ Programmable endpoint types and FIFO sizes and internal 1120-byte logical (2240-byte physical for dual-packet mode) shared FIFO storage allow a wide variety of configurations.
■ Dual-packet mode of FIFOs reduces latency.
■ Supports USB remote wake-up feature.
■ On-chip crystal oscillator allows external 12 MHz crystal or 3 V/5 V clock source.
■ On-chip analog PLL creates 48 MHz clock from internal 12 MHz clock.
■ Integrated USB transceivers.
■ 5 V tolerant I/O buffers allow operation in 3 V or 5 V system environments for 0 °C to 70 °C temperature range.
■ 5 V tolerant I/O buffers allow operation in 3 V only system environments for –20 °C to +85 °C temperature range.
■ Implemented in Agere Systems Inc. 0.25 µm, 3 V standard-cell library.
■ 44-pin MQFP (USS-820D).
■ 48-pin TQFP (USS-820TD).
■ Evaluation kit available.

New Features After Revision B
■ New, centralized FIFO status bits and interrupt output pin reduce firmware load.
■ New, additional nonisochronous transmit mode allows NAK response to cause interrupt.
■ Isochronous behavior enhancements simplify firmware control.
■ Additional FIFO sizes for nonisochronous endpoints.
■ USB reset can be programmed to clear device address.
■ USB reset output status pin.
■ Firmware ability to wake up and reset a suspended device.
■ Lower power.
■ 5 V supply no longer required for 5 V tolerant operation.

Applications
■ Suitable for peripherals with embedded microprocessors.
■ Glueless interface to microprocessor buses.
■ Support of multifunction USB implementations, such as printer/scanner and integrated multimedia applications.
■ Suitable for a broad range of device class peripherals in the USB standard.