Digilent DXC95 Manual de referencia - Página 4

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Digilab XC95 Reference Manual

Oscillator

The DXC95 board provides a socketed half-size 8-pin DIP oscillator. The board ships with a 1.8MHz

oscillator, but oscillators from 32KHz to 50MHz can easily be substituted, allowing for a wide range of

clock frequencies. The oscillator is connected to the CPLD GCK1 input (P9), it is bypassed with a

0.1uF capacitor, and it located as physically close to the CPLD as possible.

Power Supplies

The DCX95 board uses a 1.5A LM317 LDO voltage regulator to produce the 5VDC supply. The

regulator input is driven from an external DC power supply connected to the on-board 2.1mm center-

positive power jack. The regulator has 10uF of input capacitance, 20uF of local output capacitance,

and 10uF of regulation bypass capacitance. The regulator produces a stable, low noise supply using

inexpensive wall-wart power supplies, regardless of load (up to 1.5A). The regulator body is soldered

to the board for improved thermal dissipation. DC supplies in the range of 5VDC to 10VDC may be

used. Ample bypass capacitors are used around the board to decrease power supply noise. The DXC95

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

Total board current is dependant on CPLD configuration, clock frequency, and external connections. In

test circuits with approximately half the CPLD resources routed, a 1.8MHz clock source, and a single

expansion board attached (the DIO1 board), approximately 300mA of supply current is drawn from the

supply. Current is strongly dependent on CPLD and peripheral board configurations.

Pushbutton and LED

A single pushbutton and LED are provided on the board allowing basic status and control functions to

be implemented without a peripheral board. As examples, the LED can be illuminated from a signal in

the CPLD to verify that configuration has been successful, and the pushbutton can be used to provide a

basic reset function independent of other inputs. The circuit is shown below.

Rev: May 7, 2002

Vdd

Push

button

4.7K

Figure 5. Pushbutton and LED detail

www.digilentinc.com

4.7K

Xilinx

95108

CPLD

80 Ohm

Digilent, Inc.

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