Digilent X-Board - Manual (Page 4)

Digilent
X-Board Reference Manual
www.digilentinc.com
Copyright Digilent, Inc. Page 4/6 Doc: 502-107
External power sources are routed through a Linear regulator. The voltage input to the power pins is
routed to a voltage regulator that produces the supply for the board. To use an external battery
source, jumper J2 must be set to “BAT” and power applied to the J3 pins (see board silkscreen). The
regulator will handle voltages from 3.6V to 9V. If you use AA batteries, you will need to apply three in
series.
The X-Board uses a four layer PCB, with the inner layers dedicated to V
CC
and GND planes. The
CPLD and the other ICs on the board all have a complement of bypass capacitors placed as close as
possible to each V
CC
pin. The Linear regulators, together with good power supply routing and ample
bypass capacitors result in a very clean, low-noise power supply.
Clocks
The X-Board includes an user-settable silicon oscillator that produces a 1 MHz, 100 kHz, or 10 kHz
clock signal based on the position of the clock select jumper at J11 (J11 is labeled on the underside of
the board). This primary oscillator output, labeled “PCLK” in the schematic, is connected to the
GCLK2 pin of the CPLD (at P38) so that it can be routed to the internal clock divider. Pads for a
standard SMT oscillator are also provided at IC4. A 48 MHz clock is also present on P30.
10, 100 or 1000 kHz (J11) P38
48 MHz P30
Optional clock at IC4 P32
User I/O
The push buttons produce a ‘1’ to the CPLD when the button is depressed. Pushbutton switch inputs
use a series resistor for protection against short circuits (a short circuit would occur if a CPLD pin
assigned to a pushbutton was inadvertently defined as an output).
Btn0 P61
Btn1 P60
LEDs
Twelve red LEDs are provided for circuit indicators, and are user configurable. Two amber LEDs
indicate USB power (LD13) and 3.3V power (LD14) connection status. These two are fixed and
cannot be changed.
LED(0) P131
LED(1) P105
LED(2) P88
LED(3) P87
LED(4) P86
LED(5) P74
LED(6) P82
LED(7) P44
LED(8) P26
LED(9) P20
LED(10) P6
LED(11) P138