Digilent Basys Board User Manual Rev.C

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Revision: August 8, 2006 215 E Main Suite D | Pullman, WA 99163

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Overview

Digilent’s Basys circuit board is an integrated
circuit development platform based on a Xilinx
Spartan 3E Field Programmable Gate Array
(FPGA). The Basys board provides a low­cost, introductory development platform for
engineers to try new designs or learn about
FPGAs and modern CAD tools. Basys
features include:

• 100,000 gate Xilinx Spartan 3E FPGA;

• JTAG programming port;

• XCF02S Xilinx Platform Flash ROM to

store FPGA configurations;

• Large collection of I/O devices including
eight LEDs, four-digit seven-segment
display, four pushbuttons, and eight slide
switches;

• PS/2 and VGA ports;

• User-selectable oscillator

Power

jack

5-12VDC

3.3VDC

regulator

2.5VDC

regulator

1.2VDC

regulator

Clock

(100,

50, or

25

MHz)

Platform

Flash

(config

ROM)

JTAG

6-pin connectors

For A/D & D/A converters,

motor drivers, etc.

JA

JB JC

4 4 4 4

JD

(25/50/100MHz), plus a socket for a
second oscillator;

• Four 6-pin header ports for user I/O and

Featuring 4 18-bit multipliers and 9Kbytes of Block RAM

Xilinx Spartan3E-100 TQ100

peripheral module connection;

• ESD and short-circuit protection on all I/O
signals.

Functional Description

The Basys board provides an inexpensive,
robust, and easy-to-use platform that anyone

8 LEDs

4 7-seg.
displays

Figure 1: Basys block diagram

4 buttons

8 switches

PS2
Port

VGA Port

can use to gain experience with FPGA devices
and modern design methods. It is centered on
the Spartan 3E FPGA, and it contains all needed support circuits so designs can get up and running
quickly. The large collection of on-board I/O devices allow many designs to be completed without the
need for any other hardware, making the Basys an ideal introductory platform for experimenting with
new designs or learning about FPGAs and CAD tools. The four standard 6-pin expansion connectors
allow designs to grow beyond the Basys 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 Basys board
works seamlessly with all versions of the Xilinx ISE tools, including the free WebPack tools. It ships
with a power supply and programming cable, so designs can be implemented immediately without the
need for any additional hardware.

®

Copyright Digilent, Inc. All rights reserved 12 pages Doc: 502-107

Basys Reference Manual

Digilent

www.digilentinc.com

Device Configuration

At power-on, the FPGA on the Basys board is not configured and performs no functions - it 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 Basys board determines which source (PC or
ROM) the FPGA will use to load its configuration. Note that a demonstration configuration is loaded
into the Basys board during manufacturing. If that configuration has not been overwritten, it can be
automatically loaded into the FPGA by setting the Mode Select Jumper to “ROM”, and cycling power
or pressing the reset button (labeled “BTN_R”).

The FPGA and the Platform Flash ROM can be programmed from a PC using Digilent’s Adept
software or Xilinx’s iMPACT software (both are available for free download). Digilent’s JTAG3 cable
can be used to connect the board to a PC for programming with either software package.

To program the Basys board, connect the programming cable to the board
and to a PC, and apply power to the Basys board. Start the programming
software, and wait for the FPGA and the Platform Flash ROM to be
automatically identified. To program the FPGA, select the desired .bit file; to
program the Platform Flash, select the desired .mcs file. Right-click on the
device to be programmed, and select the “program” function. The
configuration file will be sent to the FPGA or Platform Flash, and the
software will indicate whether programming was successful.

Both the FPGA and Platform Flash ROM will always appear in the scan chain. After the Platform
Flash ROM has been loaded with a configuration file, the FPGA can automatically load that file at
power-on if programming mode control jumper is loaded in the ROM position.

A reset button is provided (labeled “BTN_R”) that can erase the configuration in the FPGA, and start a
new programming cycle. An LED labeled “LD_D” will illuminate whenever the FPGA has been
successfully configured.

Copyright Digilent, Inc. Page 2/12 Doc: 502-107

Basys Reference Manual

Digilent

www.digilentinc.com

Power Supply

The Basys board can be powered from any DC supply that produces a voltage in the 5VDC-12VDC
range. The power jack on the Basys board requires a center-positive, 2.1mm power supply connector
as is commonly found on wall-plug power supplies (Basys ships with a 5VDC wall-plug supply).
Voltages higher than 12V may permanently damage Basys.

The voltage input to the power jack is routed to the four 6-pin expansion connectors and to a LM1117
voltage regulator that produces the 3.3V supply for the board. The 2.5V and 1.2V supplies required by
the FPGA are produced by post-regulating the 3.3V supply. Total board current is dependant on
FPGA configuration, clock frequency, and external connections. In test circuits with roughly 20K gates
routed, a 50MHz clock source, and all LEDs illuminated, about 200mA of current is drawn from the

1.2V supply, 50mA from the 2.5V supply, and 100mA from the 3.3V supply. Required current will
increase if larger circuits are configured in the FPGA, and if peripheral boards are attached.

The Basys board uses a four 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 Basys board includes a primary, user­settable silicon oscillator that produces 25MHz,
50MHz, or 100MHz based on the position of the
clock select jumper at JP3. A socket for a second
oscillator is also provided at IC7 (the IC7 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 36 and pin 84 respectively.
Both clock inputs can drive the clock synthesizer
DLL on the Spartan 3E, allowing for a wide range
if internal frequencies, from 4 times the input
frequency to any integer divisor of the input
frequency.

User I/O

The Basys 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.

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
series resistor for protection against short circuits (a short circuit would occur if an FPGA pin assigned
to a pushbutton or slide switch was inadvertently defined as an output).

Copyright Digilent, Inc. Page 3/12 Doc: 502-107

Basys Reference Manual

Digilent

www.digilentinc.com

3.3V

Slide

switches

BTN0

BTN1

BTN2

BTN3

3.3V
SW0

SW1

SW2

SW3

SW4

SW5

SW6

SW7

69
30
13

11

98
95

94
92
91
90
89

88

Spartan 3E

FPGA

15
12
10

33
32
27
26

42
24
22
17
16
43
23
18

LD0

LD1
LD2
LD3

9

LD4

5

LD5

4

LD6

3

LD7

2

AN1

AN2

CA
CB
CC
CD
CE
CF
CG
DP

LEDs

3.3V

AN3

AN4

Sseg
Display

Outputs: LEDs

Eight LEDs are provided for circuit outputs. LED anodes are driven from the FPGA via 390-ohm
resistors, so a logic ‘1’ output will illuminate them with 3-4ma of drive current. A ninth LED is provided
as a power-on LED, and a tenth LED indicates FPGA programming status.

Outputs: Seven-Segment Display

The Basys board contains a four-digit common anode seven-segment LED display. Each of the four
digits is composed of seven segments arranged in a “figure 8” pattern, with an LED embedded in
each segment. Segment LEDs can be individually illuminated, so any one of 128 patterns can be

Copyright Digilent, Inc. Page 4/12 Doc: 502-107