## Overview of the NET2890 The **NET2890** is a high-performance **USB 2.0 Peripheral Controller** (Bridge Chip) originally designed by NetChip Technology (later acquired by PLX Technology, and subsequently Broadcom). It is primarily used to interface a local bus (like a microprocessor or DSP) to a USB 2.0 high-speed port. ### Key Technical Specifications | Feature | Specification | | :--- | :--- | | **USB Version** | USB 2.0 High-Speed (480 Mbps) and Full-Speed (12 Mbps) | | **Interface** | 8-bit or 16-bit generic local bus | | **Endpoints** | 4 Configurable Endpoints (Bulk, Interrupt, or Isochronous) | | **FIFO Memory** | 8 KB Internal RAM for data buffering | | **Voltage** | 3.3V I/O with 1.8V Core (Internal regulator usually included) | | **Package** | 80-pin TQFP or similar small footprint | --- ### Core Electronic Components & Architecture The NET2890 functions as a bridge between the **USB Serial Interface** and a **Parallel Local Bus**. Its internal architecture consists of several critical blocks: #### 1. USB Transceiver (PHY) The chip includes an integrated Physical Layer (PHY) that handles the electrical signaling of the USB bus. It manages: * Differential signaling (D+ and D-). * Automatic detection of High-Speed vs. Full-Speed connections. * Termination resistors required for USB 2.0. #### 2. Serial Interface Engine (SIE) This is the "brain" of the USB communication. It handles low-level protocols such as: * CRC generation and checking. * Packet PID decoding/encoding. * Handshaking (ACK/NAK). #### 3. Local Bus Interface The NET2890 provides a flexible asynchronous interface to connect to: * Microcontrollers (MCUs). * Digital Signal Processors (DSPs). * FPGAs. * It supports **DMA (Direct Memory Access)** transfers, allowing high-speed data movement without constant CPU intervention. #### 4. Endpoint FIFOs To maintain high-speed throughput (up to 480 Mbps), the chip uses internal **8 KB FIFO buffers**. This allows the local processor to burst data into the chip, which the NET2890 then transmits over USB whenever the host requests it. --- ### Typical Application Circuit Requirements To implement the NET2890 in a hardware design, the following electronic considerations are necessary: * **Clock Source:** Usually requires a **30 MHz crystal** oscillator to generate the internal frequencies for High-Speed USB. * **Power Decoupling:** Multiple 0.1µF and 1.0µF capacitors must be placed near the VCC pins to filter high-frequency noise. * **Termination:** While many resistors are internal, specific impedance matching (90-ohm differential) is required for the PCB traces leading to the USB connector. * **Reset Logic:** A dedicated Power-On Reset (POR) circuit or a reset pin controlled by the host MCU. --- ### Usage Example (Pseudo-Code Interface) ```c // Example: Basic register write to initialize an endpoint #define NET2890_BASE 0x8000 #define EP_CONTROL_REG (NET2890_BASE + 0x04) void init_usb_endpoint() { // Set Endpoint 1 to BULK mode and enable it uint16_t config_val = 0x0001 | 0x0080; write_local_bus(EP_CONTROL_REG, config_val); } ```