AD7303 Pmod Xilinx FPGA Reference Design

Introduction

The AD7303 is a dual, 8-bit voltage out DAC that operates from a single 2.7V to 5.5V supply. Its on-chip precision output buffers allow the DAC outputs to swing rail-to-rail. This device uses a versatile 3-wire serial interface that operates at clock rates up to 30 MHz, and is compatible with QSPIm SPI, microwire and digital signal processor interface standards.

Two reference designs are available for this part:

A design which shows how to used the AD7303 DAC by outputting square and a sawtooth waveforms
- HW Platform(s):
- System: Microblaze, AXI, UART

A design which demonstrates how to acquire a signal and reproduce it using Digilent PmodAD1 and PmodDA1. Four types of waveforms (Square, Sine, Sawtooth and Triangle) are generated using the AD7303 DAC present on the PmodDA1 board. Each waveform has a period of 25 ms, and lasts for 25 s (1000 periods). A loopback cable is connected between the output of the AD7303 DAC and the input of the AD7476 ADC present on the PmodAD1 board. The Xilinx ChipScope Analyzer tool is used to verify the digitized waveforms.
- HW Platform(s): Nexys™3 Spartan-6 FPGA Board (Digilent) PmodAD1 (Digilent) PmodDA1 (Digilent)
- System: Microblaze, AXI, UART

AD7303 Pmod Reference Design

Quick Start Guide

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).

Required Hardware

Required Software

Xilinx ISE 14.3 (Programmer (IMPACT) is sufficient for the demo and is available on Webpack).
A UART terminal (Tera Term/Hyperterminal), Baud rate 115200 for the Avnet LX-9 Microboard or 9600 for the Digilent Nexys™3 Board.

Running Demo (SDK) Program

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 (AD7303_<board_name>.zip) to the location you desire.

Avnet LX9 MicroBoard Setup

To begin, connect the PmodDA1 to J4 connector of LX9 board, pins 1 to 6 (see image below). You can use an extension cable for ease of use. Connect the USB cables from the PC to the board.

Digilent Nexys™3 Spartan-6 FPGA Board

To begin, connect the PmodDA1 to JA connector of Nexys™3 board, pins JA1 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.

FPGA Configuration

Start IMPACT, and double click “Boundary Scan”. Right click and select Initialize Chain. The program should recognize the Spartan 6 device (see screenshot below). Connect an oscilloscope to the outputs of the PmodDA1 and then program the device using the bit file provided in the project *.zip archive, located in the “sw” folder (../ad7303/sw/AD7303.bit).

If programming was successful, the Main Menu will apear in your UART terminal, as seen in the picture below. There are 3 options:

Press [1] to select Fixed Value Mode.
Press [2] to select Waveform Generation Mode.
Press [3] to select Programmable Ramp Signal Generator.

When entering Fixed Value Mode, DAC selection is automatically activated. Selecting the DAC is done by pressing [1] to [4].

Fixed Value Mode allows entering a value between 0x00 and 0xFF, value that will be programmed in the DAC. If the number of input characters is less than 2 (e.g. f or 7), the [Enter] key must be pressed in order to validate the input. If 2 characters are input, the value is automatically validated (in order to prevent entering more than 2 characters). Pressing the [s] key at any time will enter DAC Selection Mode.

Pressing the [q] key at any time exits the Fixed Value (or Waveform Generation) Mode and displays the Main Menu again.

When entering Waveform Generation Mode, DAC selection is automatically activated. Selecting the DAC is done by pressing [1] to [4].

Waveform Generation Mode allows selecting between 4 types of waveforms: Square, Triangle, Sawtooth and Sine waveforms. Changing between the 4 is done by pressing [1] to [4] on the keyboard. Pressing [s] at any time will enter DAC Selection Mode. Pressing [q] at any time will return to the Main Menu.

Programmable Ramp Signal Generator allows generating a programmable ramp signal. This mode can be used to test the PmodDA1 using a Digital Multimeter.

Enter time step allows setting a time step between 100 and 5000 ms.

Enter increment size allows selecting an increment size that suits your design. Values can vary from 0x00 to 0xFF.

Select DAC allows selecting which DAC Output will be used for the Ramp Signal Generation.

Run Ramp Signal Generator will start generating the desired output.

Using the reference design

Functional Description

The reference design is a simple SPI interface with two MOSI pins for the PmodDA1. The software programs the device sending an 8-bit configuration value followed by 8-bit data value.

The hardware SPI access allows writing data to the AD7303, using a single CS and SCLK pins, and two MOSI pins (PmodDA1 contains two AD7303 Integrated Circuits, which share the same CS and SCLK pins, but have separate MOSI pins).

Connecting the PmodDA1 to the boards using an extension cable provides ease of use.
UART must be set to 115200 Baud Rate for the Avnet LX-9 Microboard or 9600 Baud Rate for the Digilent Nexys™3 Board.

Downloads

Reference design source code for Avnet LX9 MicroBoard.
Reference design source code for Digilent Nexys™3 Spartan-6 FPGA Board.

AD7303 Pmod and AD7476 Pmod Reference Design