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This version (20 Nov 2013 15:12) was approved by Alexandru.Tofan.The Previously approved version (01 Oct 2013 08:57) is available.Diff

AD7780 Pmod Xilinx FPGA Reference Design

Introduction

The AD7780 is a complete low power front-end solution for bridge sensor products, including weigh scales, strain gages, and pressure sensors. It contains a precision, low power, 24-bit sigma-delta (Σ-Δ) ADC; an on-chip, low noise programmable gain amplifier (PGA); and an on-chip oscillator.

HW Platform(s):

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 14.4 (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 and ZedBoard 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.
If you are not familiar with ZedBoard and/or Xilix tools, please visit
http://www.em.avnet.com/en-us/design/drc/Pages/Zedboard.aspx for details.

Avnet LX9 MicroBoard Setup

Extract the project from the archive file (AD7780_<board_name>.zip) to the location you desire.

To begin, connect the PmodAD3 to J5 connector of LX9 board (see image below). 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.

PmodAD3 and LX-9

Digilent Nexys™3 Spartan-6 FPGA Board

Extract the project from the archive file (AD7780_<board_name>.zip) to the location you desire.

To begin, connect the PmodAD3 to JA connector of Nexys™3 board (see image below). 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).

PmodAD3 and Nexys™3

Avnet ZedBoard

To begin, connect the PmodAD3 to JD connector of ZedBoard (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).

PmodAD3 and ZedBoard

FPGA Configuration for Nexys3 and LX-9 MicroBoard

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 (../ad7780/sw/AD7780.bit).

Programming FPGA in IMPACT

If programming was successful, the Main Menu will appear in your UART terminal, as seen in the pictures below. There are 6 options available for you. Use [v], [f], [g], [p], [r], [s], [m] in order to choose the desired one.

Main Menu

Display Vin allows printing the input voltage over the UART with the appropriate output rate (10 Hz or 16.7 Hz, depending on Filter settings). Pressing [m] will return to menu.

Display Vin

If the device is Powered Down the user will be prompted to Power Up the device prior to trying to display the input voltage.

Display Vin error messege

Change Filter Option allows selecting between 10 Hz and 16.7 Hz Output Rate.

Change Filter Options

Change Gain Option allows selecting between a gain of 128 or a gain of 1.

Change Gain Option

Power Down / Power Up allows powering down the device or powering it back up.

Power Up/Down device

Modify Voltage Reference allows changing the voltage reference that is used to calculate the value displayed over UART. The default value is 3300 mV. If using another reference voltage, please modify it here before printing values, in order to obtain correct results. If any value besides 1 to 9 is entered, an error message will be displayed. If a value higher than 5000 is entered, an error message will be displayed. If entering less than 4 characters, please press [Enter] in order to validate your input. If 4 characters are entered, the result is automatically validated.

Modify Voltage Reference

Input errors are displayed in the following picture.

Modify Voltage Reference errors

Display current settings allows printing the current settings for the device. Any pressed key will take you back to the menu.

Display current settings

FPGA Configuration for ZedBoard

Run the download.bat script from the ”../bin” folder downloaded from the github (see the links in the download section of the wiki page). The script will automatically configure the ZYNQ SoC and download the *.elf file afterwards.

If the download script fails to run, modify the Xilinx Tools path in download.bat to match your Xilinx Installation path.

If programming was successful, you should be seeing messages appear on the terminal window. After programming the AD7780 device, the program will automatically read the value of the analog voltage input and print it via UART.

Using the reference design

Functional Description

Avnet LX-9 MicroBoard and Digilent Nexys3

The reference design is a custom communication interface, allowing control for the FILTER, GAIN, PDRST pins, reading data from the AD7780 and generating an interrupt when data has been received.

Avnet ZedBoard

The reference design is a custom communication interface, reading data from the AD7780 and generating an interrupt when data has been received. DMA transfers 256 samples from the ADC and prints the input voltage via UART. FILTER, GAIN and PDRST are hardcoded to '1', but can be easily programmed by adding links from your custom HDL to the inputs of the IPCore.

  • UART must be set to 115200 Baud Rate for the Avnet LX-9 Microboard and ZedBoard or 9600 Baud Rate for the Digilent Nexys™3 Board.
  • Reference voltage is 3300 mV default. If using another reference voltage, please check that the jumpers are properly set on the PmodAD3, and modify the reference voltage in the software application using UART (select option [r]).
  • If using 3 external signals (AVDD, AIN and REF) then 2 jumpers on PmodAD3 must be off (JP1 and JP2).
  • If using 2 external signals (AIN and REF) or (AIN and AVDD) then 1 jumper on PmodAD3 must be off (JP2 or JP1).
  • Be aware that 0.5V ≤ Vref ≤ AVDD and 2.7V ≤ AVDD ≤ 5.25V.
  • Be aware (especially when using gain = 128) that the common-mode voltage (AIN(+) + AIN(−)) / 2 must be ≥ 0.5V.

Downloads

Linux Device Driver - Custom HDL PCore

Connect PmodAD3 to the JD1 connector of the ZedBoard (upper row of pins).

Preparing the SD Card

In order to prepare the SD Card for booting Linux on the ZedBoard:

Make sure you have an HDMI monitor connected to the ZedBoard, plug in the SD Card and power on the board. If everything is correct, the system should boot up. If you don't have an HDMI monitor, connect to the board via UART, Baud Rate 115200.

There are 2 ways to test the driver.

  • Using the terminal window
  • Using the ADI IIO Oscilloscope

Using the terminal window

Open a new terminal window by pressing Ctrl+Alt+T.

Navigate to the location of the device and identify it using the following commands:

cd /sys/bus/iio/devices/
ls
iio:device0 iio:device1 trigger0
cd iio\:device0
cat name
AD7780

If the cat name command doesn't return ad7780, then change the number of the iio:device, and check again.

cd ..
cd iio\:device1
cat name

To see the list of options that the AD7780 driver provides, type:

ls
buffer  dev  name  power  scan_elements  subsystem  uevent

To read the raw input voltage, type:

cd buffer
echo 40 > length
echo 1 > enable
hexdump -x /dev/iio\:device0
0000000    d34d    7d63    d44d    7d63    d04d    7d63    c84d    7d63
0000010    d44d    7d63    d74d    7d63    e04d    7d63    d84d    7d63

AD7780 Read Voltage from Terminal

The commands written above can also be used if not using an HDMI monitor and a wireless keyboard, by using a serial terminal, and typing the commands after the system boot-up is complete.

AD7780 Read Voltage from Serial Terminal

Using the ADI IIO Oscilloscope

Install the ADI IIO Oscilloscope using the instructions from the following wiki page:

Launch the ADI IIO Oscilloscope.

Select AD7780 from the Device drop-down menu. Set the desired number of samples in the Sample Count tab. Click the Green Play Button in order to start capturing and displaying data. Click Stop to stop the process.

AD7780 IIO Oscilloscope Plot

More information