Digilent Nexys Board - Manual (Page 2)

Digilent
Nexys Reference Manual
www.digilentinc.com
Copyright Digilent, Inc. Page 2/10 Doc: 502-107
Functional Description
The Nexys board provides an inexpensive, robust, and easy-to-use platform that anyone can use to
gain experience with FPGA devices and modern design methods. It is centered on the Spartan 3
FPGA, and it contains all needed support circuits so designs can get up and running quickly. The
large collection of on-board devices allow many designs to be completed without the need for any
other hardware, making the Nexys an ideal platform for experimenting with new designs or learning
about FPGAs and CAD tools. The 100-pin high-speed connector and four 6-pin expansion connectors
allow designs to grow beyond the Nexys board, either with user-designed boards or breadboards
and/or peripheral module (Pmod) boards offered by Digilent. (Pmods are inexpensive analog and
digital I/O modules that offer A/D conversion, D/A conversion, motor drive, sensor input, and a host of
other features). Signals on each 6-pin expansion connector are protected against damage from ESD
and short-circuit connections, ensuring a long operating life in any environment. The Nexys board
works seamlessly with all versions of the Xilinx ISE tools, including the free WebPack tools. The
Nexys recieves power from the USB interface and it ships with a USB cable, so designs can be
implemented immediately without the need for any additional hardware.
FPGA and Platform Flash Configuration
The FPGA on the Nexys board must be configured (or programmed) by the user before it can perform
any functions. Design software, like the free WebPack from Xilinx, can be used to define any number
of circuits that can be programmed into the FPGA. Once programmed, the FPGA will retain its
configuration only as long is power is applied. The FPGA can be programmed in two ways: directly
from a PC, and from an on-board Platform Flash ROM that is also user-programmable. A jumper on
the Nexys board determines which source (PC or ROM) the FPGA will use to load its configuration.
The FPGA can automatically load a configuration at power-on from the Platform Flash ROM by setting
the Mode Select Jumper JP3 to “FLASH”.
Note that a demonstration configuration is loaded into the Nexys board during manufacturing. If that
configuration has not been overwritten, it can be automatically loaded into the FPGA by setting the
Mode Select Jumper JP3 to “FLASH”, and cycling power or pressing the reset button.
XCF02
Platform
Flash
JTAG3
header
Slave
Serial
JTAG
PROG
DONE
Vdd
DONE
LED
PROG
(reset)
button
Spartan 3
FPGA
Mode Select
Jumper
JTAG ROM
Configure from on-board ROM
Configure from PC via JTAG
JTAG3
header
RESET
button
DONE
LED
Mode Select
Jumper
Mode Select
Jumper