AVR ATmega32U4 used to configure the FPGA,
USB communications, and to assist with analog-to-digital conversion (ADC). Additionally, there
are eight LEDs and a pushbutton on the board
available to the user.
The Mojo V3 arose from a Kickstarter
project and boasts both open source software
and hardware. Be aware, you have to supply a
micro USB cable and an optional 5-12 VDC
power supply if you need to draw more current
than your USB port can safely provide (typically
Where Do I Begin?
There is a significant software stack in order
to begin using the Mojo V3. However, all of it is
free of charge. The first order of business is to
download ISE Design Suite 14. 7 from Xilinx (if
you cannot download the full DVD ISO, Xilinx
will mail you a DVD free of charge).
Unfortunately, the software is only for Windows
and Linux, as the world of FPGAs is not yet Mac
friendly. As a Mac user myself, I got around this
by running Linux Mint 17.1 in Parallels Desktop
10 and it works flawlessly.
If you don’t want to shell out the money for
Parallels Desktop, you should have no problem
running Linux Mint in VirtualBox. (I have been
using VirtualBox for a Windows XP virtual
machine for years.) Installation is fairly easy, but
be aware that it does take a significant amount
of space ( 20+ GB). For a detailed installation
tutorial, please see Embedded Micro’s Installing
The next piece of software you’ll need is
the Mojo Loader. This software is produced by
Embedded Micro and — once again — is only for
Windows and Linux. As with ISE Design Suite,
Embedded Micro has an excellent installation
Optional software includes the Arduino IDE
(integrated development environment) and the
Mojo IDE. If you are savvy, you can load the
onboard ATmega32U4 with custom software to
utilize the full potential of the microcontroller
for whatever you desire. I have not tried the
Mojo IDE which is designed for development
outside of the ISE Design Suite (although it is
still required for the command line tools), as it is
still very much in beta.
Project Setup Basics
Okay, with our software stack installed, let’s
design something! I think an easy starting point
is a 2-to- 4 line single bit decoder with Enable.
This project will allow us to investigate some
basic combinational logic using the Mojo V3.
However, before we can start writing hardware
(sounds weird, doesn’t it?), let’s cover the basic
steps to create a project in ISE Design Suite.
With the software open, create a new
project (File->New Project…). Name the project
binary_decoder and add /syn to the end of the
Working Directory (trust me on this… ISE loves
to make files and this will contain the mess).
Click Next (Screenshot 1).
We need to specify some project settings.
The Family should be set to “Spartan6” and the
Device to “XC6SLX9.” The Package is
“TQG144” and the Speed is “- 2.” Now, you’re
probably asking me, “How do you know the
speed is - 2?” Great question!
If you look at the FPGA package on the
Mojo V3 board, the last line of text says “2C”
(Photo 1). Reading the Spartan- 6 Family
Overview Datasheet, this indicates a speed
grade of “- 2” and a commercial temperature
July 2015 35
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