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Digilent

Nexys2 Reference Manual

www.digilentinc.com

USB Port

The Nexys2 includes a high-speed USB2

port based on a Cypress CY7C68013A USB

controller. The USB port can be used to

program the on-board Xilinx devices, to

perform user-data transfers at up to

38Mbytes/sec, and to provide power to the

board. Programming is accomplished with

Digilent's free Adept Suite Software. User

data transfers can also be accomplished

using the Adept software, or custom user

software can be written using Digilent's

public API's to access the Nexys2 USB

connection. Information on using Adept

and/or the public API's to transfer data can

Figure 11: Nexys2 USB circuit

be found on the Digilent website.

The USB port can also provide power to the Nexys2 board if the power select jumper is set to "USB".

The USB specification requires that attached devices draw no more than 100mA until they have

requested more current, after which up to 500mA may be drawn. When first attached to a USB host,

the Nexys2 board requests 500mA, and then activates a transistor switch to connect the USB cable

voltage to the main input power bus. The Nexys2 board typically draws around 300mA from the USB

cable, and care should be taken (especially when using peripheral boards) to ensure that no more

than 500mA is drawn.

PS/2 Port

The 6-pin mini-DIN connector can accommodate a PS/2 mouse or keyboard. Most PS/2 devices can

operate from a 3.3V supply, but older devices may require a 5VDC supply. A three-pin jumper on the

Nexys2 board immediately adjacent to the PS/2 connector selects whether regulated 3.3V or the main

input power bus voltage (VU) is supplied to the PS/2 connector. To send 5V to the PS/2 connector,

set the PS2 power jumper to Vswt (the main input power bus), and ensure the board is powered from

USB or a 5VDC wall-plug supply. To send 3.3V to the connector, set the jumper to 3.3V.

Figure 12: Nexys2 PS/2 circuits

Both the mouse and keyboard use a two-wire serial bus (clock and data) to communicate with a host

device. Both use 11-bit words that include a start, stop and odd parity bit, but the data packets are

organized differently, and the keyboard interface allows bi-directional data transfers (so the host

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