Maual Nexys2

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Digilent Nexys2 Board
Reference Manual

w w w. d ig i l en t inc .c om

Revision: July 11, 2011

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Overview
The Nexys2 circuit board is a complete,
ready-to-use circuit development platform
based on a Xilinx Spartan 3E FPGA. Its onboard high-speed USB2 port, 16Mbytes of
RAM and ROM, and several I/O devices andports make it an ideal platform for digital
systems of all kinds, including embedded
processor systems based on Xilinx’s
MicroBlaze. The USB2 port provides board
power and a programming interface, so the
Nexys2 board can be used with a notebook
computer to create a truly portable design
station.
The Nexys2 brings leading technologies to a
platform that anyone can use to gain digitaldesign experience. It can host countless
FPGA-based digital systems, and designs
can easily grow beyond the board using any
or all of the five expansion connectors. Four
12-pin Peripheral Module (Pmod) connectors
can accommodate up to eight low-cost
Pmods to add features like motor control, A/D
and D/A conversion, audio circuits, and a host
of sensor and actuator interfaces. All useraccessiblesignals on the Nexys2 board are
ESD and short-circuit protected, ensuring a
long operating life in any environment.
The Nexys2 board is fully compatible with all
versions of the Xilinx ISE tools, including the
free WebPack. Now anyone can build real
digital systems for less than the price of a
textbook.

• 500K-gate Xilinx Spartan 3E FPGA
• USB2-based FPGA configuration and high-speeddata
transfers (using the free Adept Suite Software)
• USB-powered (batteries and/or wall-plug can also be used)
• 16MB of Micron PSDRAM &16MB of Intel StrataFlash ROM
• Xilinx Platform Flash for nonvolatile FPGA configurations
• Efficient switch-mode power supplies (good for battery
powered applications)
• 50MHz oscillator plus socket for second oscillator
• 60 FPGA I/O’s routed toexpansion connectors (one highspeed Hirose FX2 connector and four 6-pin headers)
• 8 LEDs, 4-digit 7-seg display, 4 buttons, 8 slide switches
• Ships in a plastic carry case with USB cable
Figure 1: Nexys2 block diagram and features

Power Supplies
The Nexys2 board input power input bus can be driven from a USB cable, from a 5VDC-15VDC,
center positive, 2.1mm wall-plug supply, or from a batterypack. A shorting block loaded on the
“power select” jumper selects the power source. The USB circuitry is always powered from the USB
cable – if no USB cable is attached, the USB circuitry is left unpowered.

Copyright Digilent, Inc. All rights reserved

12 pages

Doc: 502-134

Digilent

Nexys2 Reference Manual

www.digilentinc.com

Figure 2: Nexys2 power supply block diagram

Theinput power bus drives a 3.3V voltage regulator
that supplies all required board current. Some devices
require 2.5V, 1.8V, and 1.2V supplies in addition to the
main 3.3V supply, and these additional supplies are
created by regulators that take their input from the
main 3.3V supply. The primary supplies are generated
by highly efficient switching regulators from Linear
Technology. Theseregulators not only use USB power
efficiently, they also allow the Nexys2 to run from
battery packs for extended periods.

Table 1: Nexys2 Power Supplies
Supply
3.3V main
2.5V FPGA
1.2V FPGA
1.8V SRAM
3.3V USB

Amps (max/typ)
Device
IC6: LTC1765
3A/100mA
IC7: LTC3417
1.4A/50mA
IC7: LTC3417
1.4A/200mA
IC8: LTC1844
150mA/90mA
IC5: LTC1844
150mA/60mA

Total board current dependson the FPGA configuration,
clock frequency, and external connections. In test
circuits with roughly 20K gates routed, a 50MHz clock
source, and all LEDs illuminated, about 200mA of
current is drawn from the 1.2V supply, 50mA from the
2.5V supply, and 100mA from the 3.3V supply. Required
current will increase if larger circuits are configured in
the FPGA, and if peripheral boards are...