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www. d igilent inc.com

Revision: August 18, 2007 215 E Main Suite D | Pullman, WA 99163

The Basys board is a circuit design and

implementation platform that anyone can use

to gain experience building real digital circuits.

Built around a Xilinx Spartan-3E Field

Programmable Gate Array and a Cypress EZ-

USB controller, the Basys board provides

complete, ready-to-use hardware suitable for

hosting circuits ranging from basic logic

devices to complex controllers. A large

collection of on-board I/O devices and all

using breadboards, user-designed circuit

boards, or Pmods (Pmods are inexpensive

analog and digital I/O modules that offer A/D

& D/A conversion, motor drivers, sensor

inputs, and many other features). Signals on

the 6-pin connectors are protected against

ESD damage and short-circuits, ensuring a

long operating life in any environment. The

Basys board works seamlessly with all

versions of the Xilinx ISE tools, including the free WebPack. It ships with a USB cable that provides

programmed from within the Xilinx ISE tool environment using a Digilent JTAG3 (or suitable Xilinx

cable) and a separate power supply.

The Basys board is designed to work with the free ISE WebPack CAD software from Xilinx. WebPack

can be used to define circuits using schematics or HDLs, to simulate and synthesize circuits, and to

create programming files. Webpack can be downloaded free of charge from www.xilinx.com/ise/.

The Basys board ships with a built-in self-test stored in its ROM that can be used to test all board

features. To run the test, set the Mode Jumper (see below) to ROM and apply board power. If the test

is erased from the ROM, it can be downloaded and reinstalled at any time. See

• 8 LEDs, 4-digit 7-segment display, 4 buttons, 8 slide switches

• PS/2 port and 8-bit VGA port

• User-settable clock (25/50/100MHz), plus socket for 2

clock

• Four 6-pin header expansion connectors

• ESD and short-circuit protection on all I/O signals.

Figure 1. Basys board block diagram and features

Digilent

Basys Reference Manual

The Basys board is typically powered from a USB cable, but a

power jack and battery connector are also provided so that external

supplies can be used. To use USB power, set the power source

switch (SW8) to USB and attach the USB cable. To use an external

wall-plug power supply, set SW8 to EXT and attach a 5VDC to

9VDC supply to the center-positive, 2.1/5.5mm power jack. To use

battery power, set SW8 to EXT and attach a 4V-9V battery pack to

the 2-pin, 100-mil spaced battery connector (four AA cells in series

make a good 6+/- volt supply). Voltages higher than 9V on either

pin expansion connectors and to a National Semiconductor LP8345 voltage regulator. The LP8345

produces the main 3.3V supply for the board, and it also drives secondary regulators to produce the

2.5V and 1.2V supply voltages required by the FPGA. Total board current is dependant on FPGA

configuration, clock frequency, and external connections. In test circuits with roughly 20K gates

routed, a 50MHz clock source, and all LEDs illuminated, about 100mA of current is drawn from the

1.2V supply, 50mA from the 2.5V supply, and 50mA from the 3.3V supply. Required current will

increase if larger circuits are configured in the FPGA, or if peripheral boards are attached.

The Basys board uses a four layer PCB, with the inner layers dedicated to VCC and GND planes. The

FPGA and the other ICs on the board have large complements of ceramic bypass capacitors placed

must be configured before it can perform any

useful functions. During configuration, a “bit” file

is transferred into memory cells within the

FPGA to define the logical functions and circuit

interconnects. The free ISE/WebPack CAD

software from Xilinx can be used to create bit

files from VHDL, Verilog, or schematic-based

source files.

Digilent’s PC-based program called Adept can

Platform Flash can automatically transfer a stored bit file to the FPGA at a subsequent power-on or

reset event if the Mode Jumper is set to ROM. The FPGA will remain configured until it is reset by a

FPGA Reset button

and Done LED

USB Connector

and circuit