Manual nexys2

Digilent Nexys2 Board Reference Manual
Revision: June 21, 2008

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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 and ports makeit 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 digital design experience. It canhost 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 useraccessible signals on the Nexys2 boardare 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. 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 battery pack. 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.
• 500K-gate Xilinx Spartan 3E FPGA • USB2-based FPGA configuration and high-speed data 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 to expansion 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

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Nexys2 Reference Manual

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Figure 2: Nexys2 power supply block diagram

The input power bus drives a 3.3V voltage regulator thatsupplies 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. These regulators not only use USB power efficiently, they also allow theNexys2 to run from battery packs for extended periods. Total board current depends on 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 largercircuits are configured in the FPGA, and if peripheral boards are attached. The table above summarizes the power supply parameters. The Nexys2 board can also receive power from (or deliver power to) a peripheral board connected to a Pmod connector or to the large 100-pin expansion connector. Jumpers near the Pmod connectors and large expansion connector (JP1 – JP5) can connect the Nexys2’s input...