Digilent XCRP User Manual

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Revision: 04/12/05

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Overview

The Digilab XCRP circuit board, built around
the Xilinx CoolRunner XC3064 CPLD, provides
a very low cost platform that can be used to
implement a wide variety of digital circuits,
from complex combinational devices to
sequential machines and controllers. The
XCRP board provides an ideal platform for new
engineers requiring experience with basic
digital design techniques, as well as those
needing exposure to Xilinx CAD tools and
CPLD devices. XCRP board features include:

• A socketed Xilinx XCR3064 CPLD

• Non-volatility – designs remain in the CPLD

after power is removed

• On board voltage regulator for use with a
wall-plug transformer, or the board can run

Power

jack

5-9VDC

3.3VDC

regulator

Vcc

2 AA
cells

Adjustable clock
(0. 5Hz to 4KHz)

more than 60hrs on 2 AA cells (typical)

• Expandability –an integral solderless
breadboard allows expansion circuits to be
constructed right on the XCRP board

JTAG

Port

XCR3064XL CoolRunner
CPLD PC-44 (s ock et ed)

• Four debounced buttons

• Eight slide switches

• Eight LEDs in three colors (red, green, and

yellow)

• 40-pin expansion connector

• JTAG programming using a standard

parallel cable (included)

• Two high-bright seven segment displays

8 LEDs

2 7-seg.
displays

8 switches

XCRP Circuit Diagram

Debounce

4 buttons

• An user-adjustable oscillator circuit
(approximately 0.5Hz to 4KHz).

The XCRP board makes an excellent platform
for instructional-lab based work: it is fully
compatible with all versions of the Xilinx CAD
tools, including the free WebPack tools
available at the Xilinx website; the included
CPLD uses non-volatile configuration memory,
so designs can be completed outside the lab;
and the board ships with a programming cable
and a power source, so designs can be

implemented immediately without the need for
any additional hardware.

Functional description

The XCRP board has been designed to offer a
low-cost system for designers who need a
flexible platform to gain exposure to the basics
of digital design or to CPLD devices. The
XCRP board provides sufficient I/O devices so
that many interesting circuits can be
implemented without the need for any other

Doc: 502-021 page 1 of 1

Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.

Expansion
Connector

Solderless

breadboard

®

XCRP Reference Manual Digilent, Inc.

devices. All CPLD signals are routed to an
expansion connector so that designs can
easily be extended using the on-board
solderless breadboard, or by attaching
accessory boards. The board can run on two
AA cells, so designs are portable. It includes a
XCR3064 CoolRunner CPLD, a JTAG
configuration circuit that uses a standard
parallel cable, a user-settable oscillator circuit,
and several useful I/O devices.

Table 1 shows all signals routed on the XCRP
board. These signals and their circuits are
described in the following sections.

Power Supplies
VBAT Battery voltage
VEXT External voltage applied to J4
VCC System voltage (VBAT or VEXT)
GND System ground routed to all devices
Programming parallel port
TDI JTAG data input signal
TCK JTAG clock signal
TMS JTAG test mode select signal
TDO JTAG data out signal
On board devices
MCLK Master clock from user-settable oscillator
BTN1-4 Debounced button inputs
SW1-8 Slide switch inputs
LED1-8 Individual LED drive signals
CAT1, 2 Common cathode signals for 7Seg displays
AA-AG Anode signals for seven segment displays
Expansion Connector
NA All signals routed to connector (except MCLK)

box. Attach the programming cable, and start
the iMPACT programmer. The board will be
auto-detected by the Xilinx software, and all
normal JTAG operations will be available.
Operations are available in a pull-down menu
made visible by right clicking on the device
graphic in the iMPACT programmer window.

Oscillator

The XCRP board provides an user-adjustable
oscillator that can produce a clock signal in the

0.5 to 4KHz range. The oscillator circuit uses
an auto-feedback Schmidt-trigger inverter, with
a variable resistor and fixed 4.7uF capacitor in
the feedback path. The variable resistor is a

User

Adjust

MCLK

Figure 2. Oscillator Circuit

15-turn precision potentiometer that can be
adjusted from 0 to 500K ohms, providing an
RC time constant that varies by several orders
of magnitude. This clock source provides an
adequate frequency range for experiments that

Table 1. XCRP board signal definitions

CPLD configuration circuit

The XCRP board uses a JTAG port connector
to route programming signals from a host
computer to the CPLD. The programming
circuit simply connects the JTAG port pins
driven by the Xilinx CAD tools directly to the
CPLD programming pins, making the board
fully compatible with all Xilinx programming
tools. To configure the board from a computer
using the JTAG cable, ensure the circuit is
powered either by batteries or by an external
power supply. Before running Xilinx’s iMPACT
programmer tool to download a bit file, ensure
that the JTAG start-up clock is selected in the

run from “human time” (i.e., less than 1 Hz) to
the audio range. The oscillator output drives
the CLK0 input of the CPLD via a second
Schmidt trigger.

Power Supplies

The XCRP board can be powered from any
wall-plug transformer that uses a 2.1mm
center-positive jack, and that produces at least
100mA in the 5VDC to 9VDC range. The board
can also be powered from 2AA cells or any
other power source that outputs at least
100mA at 2.5 to 4.0 volts. The secondary
power source connector bypasses the on­board regulators, so if that connector is used,
ensure that no more than 4VDC is applied to
the board. During operation, the board

“Generate Programming File” properties dialog

Copyright Digilent, Inc. Page 2/2 Doc: 502-046