The ADXL345 is a small, thin, ultralow power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16 g. Digital output data is formatted as 16-bit twos complement and is accessible through either a SPI (3- or 4-wire) or I2C digital interface. The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion or shock. Its high resolution (3.9 mg/LSB) enables measurement of inclination changes less than 1.0°.
System: Microblaze, AXI, UART
The bit file provided in the project *.zip file combines the FPGA bit file and the SDK elf files. It may be used for a quick check on the system. All you need is the hardware and a PC running a UART terminal and the programmer (IMPACT).
<note tip>If you are not familiar with LX9 and/or Xilix tools, please visit
http://www.xilinx.com/products/boards-and-kits/AES-S6MB-LX9.htm for details.
If you are not familiar with Nexys™3 and/or Xilix tools, please visit
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,897&Prod=NEXYS3 for details. </note>
Extract the project from the archive file (ADXL345_<board_name>.zip) to the location you desire.
To begin, connect the PmodACL to J5 connector of LX9 board (see image below). You can use an extension cable for ease of use. Connect the USB cable from the PC to the USB-UART female connector of the board for the UART terminal. The board will be programmed through its USB male connector.
To begin, connect the PmodACL to JA connector of NEXYS3 board (see image below). You can use an extension cable for ease of use. Connect the USB cables from the PC to the board, one for programming (Digilent USB device) and one for the UART terminal (FT232R USB UART).
Start IMPACT, and double click “Boundary Scan”. Right click and select Initialize Chain. The program should recognize the Spartan 6 device (see screenshot below). Start a UART terminal (set to appropiate baud rate) and then program the device using the bit file provided in the project *.zip archive, located in the “sw” folder (../adxl345/sw/ADXL345.bit).
If programming was successful, the Main Menu will apear in your UART terminal, as seen in the picture below. There are 7 options. Pressing [e], [d], [a], [s], [r], [t] or [q] key will allow you to select the desired option. After the end of every option, all the possible options (the Menu) will be shown again, allowing the user to make a new choice.
Enable Measurement sets the ADXL345 into measurement mode. Any measurement that takes place from that moment on will be valid data.
Disable Measurement sets the ADXL345 into standby mode. Any measurement that takes place from that moment will not be valid data (usually 0).
Display Acceleration displays acceleration data on all 3 Axes.
Select Measurement Range allows choosing between 4 options: ±2g, ±4g, ±8g and ±16g. Desired measurement range is selected by pressing  to .
Change Acquisition Rate allows choosing different Acquisition rates for the ADXL345. Desired option is selected by pressing  to .
Select Tap Interrupts allows enabling or disabling tap interrupts. Desired option is selected by pressing  to . If the tap option selected is  or , after a single tap, D2 (LX9) / LD0 (Nexys3) will be ON. If the tap option selected is  or , after two consecutive taps, D3 and D2 (LX9) / LD1 and LD0 (Nexys3) will both be on at the same time. If the tap option selected is , no LEDs will be ON after a single or double tap.
Stop any ongoing action will stop any display of measurements and afterwards display the Main Menu.
The reference design is a SPI interface used to communicate with the device. The software programs the ADXL345s internal registers, and afterwards reads desired data from the device and prints it via UART. Three Interrupt signals are used in the design: one coming from the ADXL345, one from the UART and a timer interrupt (used for single and double tap LED signaling).