The AD7991 is a 12-bit, low power, successive approximation ADC with an IIC-compatible interface. It operates from a single 2.7V to 5.5V power supply and features a 1 us conversion time. The track-and-hold amplifier allows each part to handle input frequencies of up to 14 MHz, and a multiplexer allows taking samples from four channels.
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).
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.
Extract the project from the archive file (AD7991_<board_name>.zip) to the location you desire.
To begin, connect the PmodAD2 to J5 connector of LX9 board, pins 3 to 6 (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 PmodAD2 to JA connector of Nexys™3 board, pins JA3 to JA6 (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).
If you do not use an extension cable, please connect the PmodAD2 as shown in the picture below. If you connect it using all 8 pins (inserting it completely in the Pmod connector J5 on the LX-9 Board, IIC won't work, because the second row of pins are grounded.
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 (../ad7991/sw/AD7991.bit).
If programming was successful, you should be seeing messages appear on the terminal window as shown in the figure below. After programming the AD7991 device, the program will automatically read the values of the analog voltage inputs, and print them via UART. Pressing any key will initialize another conversion on the next channel.
The reference design is a simple IIC interface for the AD7991. The software programs the device and prints the values of the analog input voltages. The information is displayed on UART.
The hardware IIC access allows reading the data sent by the AD7991 and also configuring the device, using the SCL and SDA pins.