Digilent MX4cK Manuel d'utilisateur télécharger pdf (Page 14)

Cerebot MX4cK Reference Manual

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USB Interface

The PIC32MX460 microcontroller contains a

USB 2.0 Compliant, Full Speed Device and

On-The-Go (OTG) controller. This controller

provides the following features:

• USB full speed host and device support

• Low speed host support

• USB OTG support

• Endpoint buffering anywhere in system

RAM

• Integrated DMA to access system RAM

and Flash memory.

The USB controller uses a phased lock loop,

PLL, to generate the necessary USB clock

frequency from the external primary oscillator

input frequency. By default, this PLL is

disabled. In order to use the USB controller, it

is necessary to enable the USB PLL, and set

the input divider to the correct value to

generate a valid USB clock. The input to the

USB PLL must be 4Mhz. The Cerebot MX4cK

provides an 8Mhz clock to the PIC32

microcontroller, so a USB PLL input divider

value of 2 must be used. These parameters

are set in the PIC32 microcontroller

configuration registers using the

#pragma

config

statement. The following statements

must be used to configure the PIC32

microcontroller for use of the USB controller:

#pragma config UPLLEN = ON

#pragma config UPLLIDIV = DIV_2

When using the chipKIT MPIDE development

environment, these will have been set by the

boot loader, so no action is needed.

When operating as a USB device, the Cerebot

MX4cK can be operated as a self-powered

device or as a bus powered device. To

operate as a self-powered device, an external

power supply should be connected to one of

the external power connectors (J13, J14 or

J18) and a shorting block placed on the “EXT”

position of J12. The external power supply

must be a regulated 5V supply. To operate as

a USB bus powered device, the shorting block

should be placed in the USB Device position,

“USB”, on J12.

Note that when operating as a bus powered

device, the Cerebot MX4cK and all devices

connected to it are limited to no more than

500mA of current.

Connector J15, on the bottom of the board in

the lower right corner is the Device/OTG

connector. This is a standard USB micro-AB

connector. Connect a cable with a micro-A

plug (optionally available from Digilent) from

this connector to an available USB port on a

PC or USB hub for device operation.

When operating as a USB host, the Cerebot

MX4cK must be externally powered. Connect

a regulated 5V power supply to one of the

external power connectors (J13, J14, or J18)

and ensure that the shorting block is in the

center, “EXT” position of J12. The power

supply used must be a regulated 5V supply.

The Cerebot MX4cK board provides power to

the attached USB device when operating as a

host, and the USB specification requires the

use of a 5V power supply. NOTE: Providing a

voltage greater than 5V can damage the

Cerebot MX4cK board and/or the USB device

being used.

Connector J17, on the top of the board in the

lower right corner is the USB host connector.

This is a standard USB type A receptacle. USB

devices may be connected either directly or

through a standard USB cable.

Jumper JP6 is used to route power to the host

connector being used. Place the shorting

block in the “HOST” position when using the

standard USB type A (host) connector, J17.

Place the shorting block in the “OTG” position

for use with the USB micro-AB (OTG)

connector, J15.

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