Nexys2 Reference Manual
Digilent
www.digilentinc.com
Copyright Digilent, Inc.
Page 4/17
Doc: 502-134
Figure 5: Nexys2 board programming circuits
Figure 7: Nexys2 board I/O devices
“done” LED will illuminate after the FPGA has been
successfully configured. For further information on
using Adept, please see the Adept documentation
available at the Digilent website.
The Nexys2 board can also be programmed using
Xilinx’s iMPACT software by connecting a suitable
programming cable to the JTAG header. Digilent’s
JTAG3 cable or any other Xilinx cable may be
used.
A demonstration configuration is loaded into the
Platform Flash on the Nexys2 board during
manufacturing. That configuration, also available
on the Digilent webpage, can be used to check all
of the devices and circuits on the Nexys2 board.
Clocks
The Nexys2 board includes a 50MHz oscillator and a socket for a
second oscillator. Clock signals from the oscillators connect to
global clock input pins on the FPGA so they can drive the clock
synthesizer blocks available in FPGA. The clock synthesizers
(called DLLs, or delay locked loops) provide clock management
capabilities that include doubling or quadrupling the input
frequency, dividing the input frequency by any integer multiple,
and defining precise phase and delay relationships between
various clock signals.
User I/O
The Nexys2 board includes several input devices, output devices, and data ports, allowing many
designs to be implemented without the need for any other components.
Inputs: Slide Switches and Pushbuttons
Four pushbuttons and eight slide switches are provided for circuit inputs. Pushbutton inputs are
normally low, and they are driven high only when the pushbutton is pressed. Slide switches generate
constant high or low inputs depending on their position. Pushbutton and slide switch inputs use a
Figure 6: Nexys2 clocks
