USB Overview and EZ-USB 2131Q Chip

USB Overview and EZ-USB 2131Q Chip Introduction

Universal Serial Bus is suitable for connecting USB peripheral devices to the host, and realizes data transmission through the PCI bus and the system bus inside the PC. At the same time, USB is also a communication protocol that supports data transmission between the host system and its peripheral devices. In the USB network protocol, each USB system can only have one host.

1.1 Basic Characteristics of USB

USB is a layered star topology, with the host controller at its root. USB devices are directly connected to the root interface to implement their functions. If multiple devices perform their functions at the same time, they must be expanded through a hub, but the expansion layer cannot exceed 5 layers. USB devices support hot plugging and can be plug and play. USB generally supports two transmission speeds, namely low speed 1.5Mbit/s and high speed 12Mbit/s. In the USB2.0 version, its speed is increased to 480Mbit/s.

USB is connected via four cables, two for power and two for differential data (D+ and D-). The host is the center of USB communication, controlling and time-sharing connected devices. The host is the only one that can use system resources. The host controller initiates transactions via the root hub. The host controller starts a frame every millisecond (in USB2.0, a frame is called a microframe every 1/8 millisecond). In this frame or 1/8 frame, the peripheral communicates data with the host. The host conducts transactions with multiple peripherals and time-shares the bandwidth requested by the peripherals.

USB has four transmission modes for different types of data. Control transmission is mainly used for settings, commands and status information; interrupt transmission is different from the general interrupt concept and is mainly used for the transmission of small amounts of data such as keyboards and mice; batch transmission is mainly used for the transmission of large amounts of data such as printers and scanners; synchronous transmission is used for real-time transmission of video, sound, etc.

In synchronous transmission mode, data transmission maintains a fixed bandwidth and delay, ensuring the stability of data transmission rate.

USB has many advantages and is suitable for the interface with video computer eyes.This paper uses a USB chip with a built-in microcontroller to design a single-chip solution for synchronous transmission.

Generally speaking, there are two types of USB control chips. One is a product with MCU (microcontroller) integrated in the chip; the other is a separate chip that implements the USB Engine function.

Considering the high transmission rate of USB, if a chip that only implements the Engine function is used, plus an ordinary microcontroller (such as 8051), its processing speed will be very slow and cannot meet the USB transmission requirements. One of the purposes of USB peripherals as consumer products is to reduce product costs. If a high-speed microprocessor (such as DSP) is used, the USB transmission rate is met, but the cost is higher. After comparing all aspects, the chip EZ-USB 2131Q with a built-in microcontroller was selected.

1.2 Introduction to the EZ-USB 2131Q chip.

The internal block diagram of EZ-USB 2131Q is shown in Figure 1. It is an 80-pin USB chip with a built-in microcontroller from Anchor Corporation, which includes three 8-bit multi-function ports, an 8-bit data port, a 16-bit address port, two USB data ports and other input and output ports.

It uses an internal RAM-based solution that allows customers to continuously configure and upgrade at any time without being restricted by port data, buffer size, transmission speed and transmission method.

The chip has an enhanced 8051 microcontroller embedded in it, and its 4 clock cycles make it 3 times faster than the standard 8051.

EZ-USB 2131Q has two synchronous transmission modes: normal read/write mode and fast read/write mode. In normal read/write mode, the chip reads or writes data from or to the outside at a rate of no more than 1000 bytes/ms, and data transmission instructions can only be listed one by one, with a total of 1000 lines of the same instructions to be written. Data cannot be transmitted in a loop in the middle, and there is no time to add other instructions. This method is not advisable for devices that require synchronous transmission and 1023 bytes per frame. In fast read/write mode, the chip can read or write 1023 bytes of data from or to the outside within 0.5ms, and there is still enough time to add other instructions.