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Digilab XC95 Reference Manual

Functional description

The Digilab DXC95 board has been designed to offer a low-cost and minimal system for designers

who need a flexible platform to gain exposure to Xilinx CPLDs, or for those who need to prototype

CPLD-based designs rapidly. The DXC95 board also has an external JTAG port – in a lower-cost

configuration, the board can be used to program Digilab peripheral boards (such as the DIO2 or AIO1

boards). The DXC95 board provides only the essential supporting devices for the 95108 CPLD, and

routes all available CPLD signals to standard expansion connectors. Included on the board are a 5VDC

regulator, a JTAG configuration circuit that uses a standard parallel cable, a 1.8MHz oscillator, and a

pushbutton and LED for rudimentary I/O.

The DXC95 board has been

designed to serve as a host for

various peripheral boards. The

expansion connectors on the

board mate with standard 40-pin,

100 mil spaced DIP headers

available from any catalog

distributor. Each of the expansion

connectors provides the

unregulated supply voltage (VU),

5V, GND, and 37 CPLD signals

to peripheral boards, so system

designers can quickly develop

application- specific peripheral

boards. Digilent also produces a

collection of expansion boards

with commonly used devices. See

the Digilent website

(www.digilentinc.com) for a

listing of currently available

boards.

Table 1 shows all signals routed on the DXC95 board. These signals and their circuits are described in

the following sections.

Parallel port and FPGA configuration circuit

The DXC95 board uses a DB-25 parallel port connector to route JTAG programming signals from a

host computer to the CPLD and to the F expansion connector. Three-state buffers, controlled by an

user-settable switch, determine whether the JTAG port is mapped to the on-board device or to the

expansion connector. With this circuit, the on-board CPLD or a peripheral board CPLD can be

configured using the JTAG protocol over the parallel cable. The JTAG programming circuit follows

the schematic available from Xilinx, so the DXC95 board is fully compatible with all Xilinx

programming tools. The JTAG circuit is shown in the diagram below.

Rev: May 7, 2002

Power Supplies

Unregulated power supply voltage – depends on power

supply used. Must be between 5VDC and 10VDC. Routed to

regulators and expansion connectors only.

VCC

VCC for all devices, routed on inner PCB plane. 1.5A can be

drawn with less than 20mV ripple (typical)

GND

System ground routed to all devices on PCB ground plane

Programming and parallel port

PWT

Feedback of TDO signal

PPO

Cable detect signals used by Xilinx programmer

TMS-L

Local TMS signal (used for JTAG programming)

TCK-L

Local TCK signal (used for JTAG programming)

TDI-L

Local TDI signal (used for JTAG programming)

TMS-E

External TMS signal (used for JTAG programming)

TCK-E

External TCK signal (used for JTAG programming)

TDI-E

External TDI signal (used for JTAG programming)

On board devices

BTN1

Pushbutton input

LED1

User-controllable status LED

MCLK

CMOS oscillator connected to global clock input

Expansion Connectors

E4-E40

E bus signals connecting the E connector to the FPGA

F4-F40

F bus signals connecting the F connectors to the FPGA

Table 1. DXC95 board signal definitions

www.digilentinc.com

Digilent, Inc.

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