“USB3.0 high-speed data acquisition system, with its 5Gbps bandwidth and superior performance such as plug and play, has attracted more and more attention. At present, the commonly used USB3.0 communication chips mainly include the EZ USB FX3 series chips developed by Cypress in the United States and the uPD720200 series chips developed by NEC in Japan.
USB3.0 high-speed data acquisition system, with its 5Gbps bandwidth and superior performance such as plug and play, has attracted more and more attention. At present, the commonly used USB3.0 communication chips mainly include the EZ USB FX3 series chips developed by Cypress in the United States and the uPD720200 series chips developed by NEC in Japan. Both of them not only have the advantages of high integration, powerful functions, and USB2.0 compatibility, but also both manufacturers provide powerful development kits, which can greatly shorten the development cycle, and are deeply loved by developers. At present, some acquisition systems use traditional 51 series single-chip microcomputers as the main control chip, which cannot fully utilize the bandwidth of USB3.0 and has poor performance. Although the CPLD chip can work at a very high frequency, it is not as flexible and easy to use as the single-chip microcomputer. Therefore, this article uses the latest high-speed ADS7886 chip of American TI company as the A/D conversion chip, the latest MSP430 single-chip microcomputer as the main control chip, and the UPD720200 of NEC company as the main control chip. USB3.0 communication chip, research and design a set of temperature data acquisition system based on USB3.0 bus. After testing, this system can realize high-speed temperature data collection.
1 System hardware design
The overall framework of the system is shown in Figure 1. The signal collected by the temperature sensor is converted into a digital signal by the A/D conversion chip ADS7886, and then sent to the main control chip MSP430, and then sent to the USB3.0 host interface chip uPD720200 after processing, and finally the data is sent to the USB host at a speed of 5Gbps .
1.1 A/D module
This module uses the latest high-speed A/D sampling chip ADS7886 from TI. ADS7886 is a 12-bit serial high-speed precision A/D chip. In order to improve the accuracy of the system, we designed the REF3030 chip to provide a 3V reference voltage. The third pin of A DS7886 is the analog signal input port, the fourth pin is the 1MHz working clock signal input port, the sixth pin is the chip select signal terminal, and the fifth pin is the output terminal after the analog signal is converted to the digital signal for MSP430 Read by the microcontroller.
1. 2 MSP430 minimum system module
The minimum system of MSP430 is shown as in Fig. 3, it is mainly composed of MSP430 one-chip computer, crystal oscillator circuit and power source. Among them, P1.4 is the ADC7886 serial data input terminal, P2.0～P2.3 are used to connect the USB3.0 communication chip uPD720200, P1.6 and P1.7 are connected to two LED indicators to Display the current working status .
1.3 USB transmission module
The module is shown in Figure 4. We have selected NEC’s uPD720200 as the USB3.0 communication chip, which fully complies with the USB3.0 communication protocol and interface specifications. The pins U3TXDP1, U3TXDN1, U3RXDP1, U3 RXDN1 of uPD720200 are connected to the pins P2.0～P2.3 of MSP430 respectively.
Its working principle is as follows: when collecting data, after uPD720200 receives the user’s data collection request, it will form the corresponding control signal, and pass it to MSP430 through P2.2 and P2.3; MSP430 then sends out the control signal for collecting data to ADS7886, And upload the data collected by ADS7886 to uPD720200 through P2.0 and P2.1; the SIE (Serial Interface Engine) of uPD720200 sends the data into the designated receiving buffer for the USB host computer to read.
2 System software design
The development of the system software includes the development of firmware programs for MSP430 and uPD720200, the development of windows driver programs for uPD720200, and the development of USB host computer application programs. We can use the development kit provided by NEC to greatly shorten the development cycle and improve development efficiency.
The MSP430 firmware program mainly completes the control of the A/D chip ADS7886 and the communication with the uPD720200 chip, which transmits the data collected by the ADS7886 chip to the uPD720200. The firmware development of MSP430 needs to define the corresponding pin and sequence, for this we use C51 language to write, the development environment is Keil uVision4.0. The main function of the uPD720200 firmware program is to allow it to transmit the data from the MSP430 chip to the upper computer to achieve ultra-high-speed data transmission. uPD 720200 fully complies with the USB3.0 protocol, and the firmware program is mainly for setting and operating its internal control registers. NEC provides developers with a powerful uPD720200 SDK development kit, which can easily develop its firmware and Wind ows driver. In the development of the application program of the upper computer, NEC company also provides users with the corresponding simple operation and powerful C++ programming interface library functions. We chose Microsoft Visual Studio2008 as the development tool, and passed the data through the corresponding library functions and device drivers to realize the real-time data collection function.
This article introduces in detail the design and development of a USB3.0 temperature acquisition and transmission system using uPD720200 as the interface USB3.0 chip and MSP430 as the main control chip. NEC provides a complete SDK development kit for uPD720200, which shortens the development cycle. The MSP430 series single-chip microcomputers we use are driven by a 25MHz crystal to achieve a 40ns instruction cycle, coupled with a 16-bit data width, its operation speed is very fast compared to the traditional 51 series single-chip microcomputers, and can give full play to the bandwidth of USB 3.0. Although affected by the sampling rate of the ADS7886 chip, over-speed data acquisition is not achieved, the combination of MSP430 and uPD720200 is undoubtedly an excellent solution for the development of high-speed data acquisition systems at a low cost and high efficiency.