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AD5628 Pmod Xilinx FPGA Reference Design

Introduction

The AD5628 The AD5628 is a low power, octal, 12 bit, buffered voltage-output DAC. The device operates from a single 2.7 V to 5.5 V supply and is guaranteed monotonic by design. The AD5628 is available in both a 4 mm × 4 mm LFCSP and a 16-lead TSSOP. The AD5628 has an on-chip reference with an internal gain of 2. The AD5628 has a 1.25 V 5 ppm/°C reference, giving a full-scale output range of 2.5 V; the AD5628-2 has a 2.5 V 5 ppm/°C reference, giving a full-scale output range of 5 V. The on-board reference is off at power-up, allowing the use of an external reference. The internal reference is enabled via a software write.

HW Platform(s):

System: Microblaze, AXI, UART

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 13.2 (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 (AD5628_<board_name>.zip) to the location you desire.

Avnet LX9 MicroBoard Setup

To begin, connect the PmodDA4 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 PmodDA4 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 following outputs of PmodDA4: A,C,E,G. Program the device using the bit file provided in the project *.zip archive, located in the “sw” folder (../ad5628/sw/AD5628.bit).

If programming was successful, the Main Menu will apear in your UART terminal, as seen in the picture below. The user has 2 options:

Press [1] to select Fixed Value Mode.
Press [2] to select Waveform Generation Mode.

When entering Fixed Value Mode, the user is automatically prompted to select which DAC will be updated. Selecting the DAC is done by pressing [1] to [9].

Fixed Value Mode allows the user to enter a value between 000 and FFF, value that will be programmed in the DAC. If the user types less than 3 characters (e.g. ff or 76), it is required to press the [Enter] key in order to validate the input. If the user types 3 characters, the value is automatically validated (in order to prevent entering more than 3 characters). Pressing the [s] key at any time will allow the user to select another DAC.

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, the user is automatically prompted to select which DAC will be updated. Selecting the DAC is done by pressing [1] to [9].

Waveform Generation Mode allows the user to select 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 allow the user to select another DAC. Pressing [q] at any time will return to the Main Menu.

Using the reference design

Functional Description

The reference design is a simple SPI interface used to communicate with the PmodDA4. The software programs the device sending 12-bit data values read from the keyboard input or from predefined look up tables. The user has the ability to select between two modes: a Fixed Value Mode or a Waveform Generation Mode. Communication between the user and the board is done via UART.

Connecting the PmodDA4 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.

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Table of Contents

AD5628 Pmod Xilinx FPGA Reference Design

Introduction