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Data acquisition system and USB interface design circuit

Published on Oct 29 2010 // Micrcontroller circuits

Data acquisition system and  USB interface design circuit

Abstract: The low-power data acquisition system of illegal income USB communication interface design. The design of the main ultra-low power MCU MSP430F13X control chip, the main control chip, connected Cygnal’s switch to USB UART chip CP2101, low-power data acquisition system USB interface design. In the IAR Embedded Workbench integrated development environment and VC + + environment, edit the MCU and the host communication protocol. The design of ultra-low power, high integration and the advantages of simple design, suitable for the development and application of portable electronic devices.
Minimum power consumption for system operation is the common approach of modern electronic systems, but also the basic requirements of green electronics. Adopt a minimum-power design method can reduce the use of power electronic equipment, and reducing power consumption under standby. As well as saving energy helps to reduce the electromagnetic pollution and is conducive to the direction of the development of portable electronic systems to help improve system reliability.
Modern industrial production and scientific research on increasing the data collection requirements. In many cases require the data acquisition system to the direction of the development of portable, requires a system with small size, low power consumption, fast transfer rates, easy to use and flexible features. In the data acquisition system, how to save energy in order to make the system work longer hours, and how communication can make the system faster data transmission has become the system development process must be considered the main content.
MSP430 ultra-low power microcontroller technology is unique in many microcontroller, and it has a high degree of integration and so on, therefore, use the controller as the system’s main controller, data acquisition and Flash memory and other functions. In addition, USB port and before the regular ports (serial and parallel port), compared with a transmission speed, low power consumption, support plug and play, and easy maintenance; so in communication design, combined with the chip CP2101 USB UART transfer in order to achieve USB interface communication. The design of both the use of the MSP430 ultra-low power consumption, and use of the CP2101 USB interface, easy design, design data acquisition systems can be highly portable, low power consumption, easy to use and other goals.
1 MSP430 USB data acquisition system interface design
1.1 Introduction admissible
This system is multi-channel data acquisition, Flash memory and USB communications and other functions. Information collection system is mainly to complete single chip, A / D conversion, the signal amplifying and filtering processing, data communications, Flash memory, etc.; real-time clock record the time data collection; CP2101 implement USB interface and the microcontroller’s signals to the microcomputer collected; completion of data receiving computer, stored in the database, data processing, computing, display and other functions.
1.2 Ultra-Low Power MSP430 Microcontrollers
TI MSP430 is introduced in recent years, the company’s 16-bit series of microcontrollers. It uses the latest low power technology, work in the 1.8 ~ 3.6V voltage, a normal operating mode (AM) and 4 low-power mode (LPM1, LPM2, LPM3, LPM4); in the current voltage of 3V, various modes of operating current, respectively AM: 340µA, LPM1: 70µA, LPM2: 17µA, LPM3: 2µA, LPM4: 0.1µA, and can easily switch between various operating modes. It’s time for low power consumption of the practical applications, especially battery-powered portable devices is particularly prominent. After initializing the system into standby mode, when there are allowed to interrupt request, CPU time in 6µ be awakened into active mode, interrupt service routine. Is finished, the RETI instruction, the system returns to the state before the interruption, continued low-power mode.
This design uses MSP430F13X microcontroller. It has a very high level of integration, monolithic integration of multi-channel 12-bit A / D converter, PWM timers, hypotenuse A / D conversion, on-chip USART, Watchdog timer, on-chip digitally controlled oscillator (DCO ), a large number of I / O ports, high-capacity on-chip RAM and ROM, and Flash memory. Flash memory, which can power-off protection and software upgrades.
1.3 USB interface chip selection
USB universal serial bus developed by Intel and other vendors have a USB connection to computer interface for communication between a variety of serial peripheral bus. Traditionally, USB interface development is more complex. At the same compared to the other after the USB interface chip, the design requires no external components selected transfer USB UART chip CP2101. Choose this interface chip, enables USB communication interface design becomes very easy. Compared with similar products, CP2101 has the following advantages:
has a smaller package. CP2101 28 pin 5mm × 5mm MLP package. This is the size of the PCB, to about 30% smaller than the competition.
height into degrees. 512 bytes of on-chip integrated EEOROM (used to store data such as manufacturer ID), an integrated transceiver chip, no external resistors;-chip clock, no external crystal.
low cost, enabling USB to serial solutions. CP2101’s USB capabilities without external components, and most of its competitors in the USB device you need additional terminal transistors, pull-up resistors, crystal, and EEPROM. Price competitive devices, simplifying the external circuit, no-cost driver support makes the CP2101 in the cost advantage is far more than competitors solutions.
low-power, high-speed characteristics, in line with USB2.0 specification, suitable for all the UART interface (baud rate 300bps ~ 921.6kbps). Industrial temperature range -40 ? ~ 85 ?).
2 USB communication interface circuit
Hardware shown in Figure 1. CP2101 The SUSPEND and SUSPEND pin to MSP430F13X ordinary serial port. The two pin USB suspend and resume sending signals, this function CP2101 device and external circuitry to facilitate power management. When the bus hangs signal is detected, CP2101 will enter Suspend mode, you can save energy. When entering suspend mode, CP2101 will issue a SUSPEND and SUSPEND signals. To avoid the SUSPEND and SUSPEND is high during reset, use 10kO pull-down resistors to ensure SUSPEND is low during reset.
CP2101’s USB function controller manages all USB and UART data transfer between, and by the USB host controller to issue the command requests and commands used to control functions such as UART. CP2101’s UART interface to handle all of the RS232 signals, including control and handshaking signals. The VBUS pin and VREGIN CP2101 must always be connected to the USB VBUS signal. Increase in VREGIN input decoupling capacitors (1µF and 0.1µF in parallel). CP2101 is a standard UART interfaces with the microcontroller level, and calculation of the USB port connection is USB standard circuit, therefore, whether 3V or 5V power supply and microcontroller connections do not need level conversion.
3 USB Communication Interface Software Design
USB interface program design includes three parts: microcontroller program development, USB device driver development, host, application development. Configure each other to complete the three reliable, fast data transfer. Cygnal USB device driver which has to provide. Here is the rest to be prepared in two parts. SCM MSP430F13X part of the serial communication program, that the baud rate, data bits, parity bit, with or without parity, design and communication protocols such as Serial communication controller settings; the other part is the host of the CP2101 communication program, this part of the VC + + environment to call the API function implementation.