Usb Bus-based Home Monitoring Data Acquisition System Design

The article introduces one home monitor data acquisition system, designed over USB bus interface based on Microsoft Windows98/2000 platform of personal computer. The main goal makes home monitor system more economical, practical and easy to operate. As a kind of novel PC bus interface specification, Universal Serial Bus is perfectly adapted to become communication interface in the middle of host and medical instrument. This system takes full advantage of Universal Serial Bus data - transmission capability. It can connect with all kind of desk PC, pocket PC and constitute high performance data acquisition measure instrument. This instrument has advantages of elaborated, easy to link, none of external power, plus and play, PnP, dynamic loading driver of USB instrument. Link and communication of host and household ward system become simple, fast and reliable. Data acquisition mode based on USB is very suited as home monitor system.This system includes hardware design, Firm Ware program design and device driver program design based on WDM. It can most support 8 channels data acquisition. Sampling frequency is 20 ~ 1 KHz per one channel and sampling precision is 8 bits.The hardware of this Data acquisition system has three parts. Fist part, A/D conversi6n chip (8 - bit A/D converter - ADC0809 uses successive approximation as conversion technique) has 8 - channel multiplexer and microprocessor compatible control logic; Second part, data buffers is IDT7205 ( 8K x 9) , which is dual - port buffers with internal pointers that load and empty data on first - in/first - out basis. Data is toggled in and out of the device through the Write ( W) and Read (R) pins. The Write -operating and Read -operating is inde-pendent each other. IDT7205 enable the data - hulk continually acquired. Third part, USB interface chip is PDIUSBD12( parallel interface) manufactured by PHILIPS. Its mostly responsible for communication between data acquisition system and host. PDIUSBD12 follows Universal Serial Bus specification revision 1.1, supporting 12Mbps full speed transfer and four kinds of transfer types. It has three end-points. Except for endpoint 0, every endpoint can be configured freely transfer type and transfer direction. In addition, it integrates 320 bytes of multi - configuration FIFO memory and offers two sets of FIFO data buffers for every endpoint. The theory of operation; under the control of 89C52(MCU) , 8 -channel multiplexer in ADC0809 switch one channel. The results of A/D conversion will be automatically written into IDT7205. The 89C52 will read data from IDT7205 and send it to host through PDIUSBD12.Firm Ware program is designed with C51 programming language. The firmware mainly performs two tasks. One is to control A/D sampling with desired sampling speed, the other is to control communication between PDIUSBD12 and host. For the first task, we use the timer Tl to time interruption. Set Tl to mode 2 and interrupt priority level to high. When the timing interruption happens, the 89C52 will update the sampling channel arid trigger ADC0809 sampling. For the second work, the firmware of PDIUSBD12 is designed to be fully interrupt - driven. While CPU is doing its foreground task, the USB transfer is being handled in the background. This assures best transfer rate and better software structure and also simplifies programming and debugging. The data exchange between the background ISR (Interrupt Service Routine) and the foreground Main Loop is achieved by event flags and data buffers. With this structure, the Main Loop does notcare whether the data source is from USB, serial port, or parallel port. The Main Loop only checks the circular buffer for new data to be processed. This concept is very important. Thus, the Main Loop program can target on data processing and the ISR can do the job of data transfer at the fastest speed possible. Similarly, the control endpoint uses the same concept in data packet handling. The ISR receives and stores control transfers in data buffers and sets the corresponding flag reg...