Digilent Nexys Board - Manual (Page 4)

Digilent
Nexys Reference Manual
www.digilentinc.com
Copyright Digilent, Inc. Page 4/10 Doc: 502-107
The Nexys board uses a six layer PCB, with the inner layers dedicated to VCC and GND planes. The
FPGA and the other ICs on the board all have a large complement of bypass capacitors placed as
close as possible to each VCC pin. The power supply routing and bypass capacitors result in a very
clean, low-noise power supply.
Oscillators
The Nexys board includes a primary, user-
settable silicon oscillator that produces 25MHz,
50MHz, or 100MHz based on the position of the
clock select jumper at JP4. A socket for a second
oscillator is also provided at IC11 (the IC11
socket can accommodate any 3.3V CMOS
oscillator in a half-size DIP package).
The primary
and secondary oscillators are connected to global
clock input pins at pin A8 and pin R9 respectively.
Both clock inputs can drive the clock synthesizer
DLL on the Spartan 3, allowing for a wide range
of internal frequencies, from 4 times the input
frequency to any integer divisor of the input
frequency.
User I/O
The Nexys board includes several Input and Output devices, and several data ports so that many
designs can be implemented without the need for any other components.
Spartan-3E
FPGA
A8 CLK_OUT
Linear Tech.
LTC6905
Oscillator
Frequency
Select
Jumper
25MHz
50MHz
100MHz
Oscillator
Socket
CLK_OUT R9