Digilent chipKIT Network Shield Довідковий посібник та керівництво користувача - Сторінка 5

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chipKIT Network Shield Reference Manual

protocol documentation, for operation of the

Ethernet interface.

The PIC32MX795 microcontroller provides two

alternate sets of pins that can be used to

connect the MAC to the external PHY. It also

provides two alternate standard MAC/PHY

interface signaling conventions. The chipKIT

Max32/Network Shield are designed to use the

standard (not the alternate) pins, and to use

the RMII (not the MII) interface signaling

convention. These options are selected using

the configuration variables in the PIC32

microcontroller and are specified using the

#pragma config

statement. To enable the

Ethernet controller in the correct configuration,

the following statements must appear in the

main program module:

#pragma config FETHIO=ON

#pragma config FMIIEN=OFF

The boot loader in the chipKIT Max32 board

sets this configuration by default. When using

the Network Shield within the MPIDE

environment no additional work is necessary.

When using it outside the MPIDE environment,

these configuration settings must be made.

The LAN8720 PHY has a reset signal, labeled

NRST in the schematic, that is used to reset

the PHY. This signal is connected to the

INT2/RE9 pin on the PIC32 microcontroller.

This pin is chipKIT digital pin 7 on the Max32

board. The NRST signal is active low.

Configure the microcontroller pin as an output

and drive it low to reset the PHY, or drive it

high to allow the PHY to come out of reset and

begin operation. The NRST signal is pulled low

on the Network Shield board, so that the PHY

is held in reset by default. To allow the PHY to

operate, this pin must be driven high. This

reset operation is not part of the Microchip

network protocol stack, and so driving NRST

high must be done before initializing the

Microchip network stack. When using the

chipKIT Ethernet library for the Network Shield,

this is done automatically by the library.

www.digilentinc.com

USB Interface

The PIC32MX795 microcontroller on the

Max32 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.

Connector J4 on the top left side of the board

is a standard USB type A receptacle. This

connector will generally be used when the

Max32/Network Shield has been programmed

to operate as a USB host. The USB device is

connected either directly, or via cable to this

connector.

Connector J2, on the bottom left side of the

Network Shield board 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 the USB controller in the PIC32

microcontroller on the Max32 board is in use, it

takes over the use of several of the pins. The

signals provided by these pins appear on

connector J13 on the Network Shield

(connector J9 on the Max32). Two addition

signals are used, when doing USB hosting.

These signals appear on AN5 and digital pin 2.

These pins are not available when using the

USB interface.

When operating as a USB device, the chipKIT

Max32/Network Shield will normally be a self

powered device. To operate as a self powered

device, an external power supply should be

connected to the external power connector, J2

on the Max32 board. If the external power

supply is a regulated 5V supply, jumper JP1 on

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