Digilent chipKIT Network Shield Manuale di riferimento - Pagina 4

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chipKIT™ Network Shield™ Reference Manual

not available for other uses, and nothing should be connected to them to avoid interference with the operation of

the Ethernet interface.

All devices on an Ethernet network must have a unique address. This address is used to direct packets on the

network to a specific device and to identify the device that originated a packet. An Ethernet MAC uses a 48-bit

address value, commonly called the 'MAC Address'. These address values are globally unique to ensure that no two

devices on a network can have conflicting addresses. MAC addresses are assigned by the IEEE. The address to use

with the Network Shield is printed on a sticker attached to the bottom of the board. The address is a twelve-digit

hexadecimal number of the form: 00183Exxxxxx, where xxxxxx represents six hexadecimal digits. This value is used

to initialize the Ethernet Controller MAC Station Address registers in the Ethernet controller of the PIC32MX795

microcontroller.

In order to connect to and use an Ethernet network, the PIC32 microcontroller must be running network protocol

stack firmware. Normally, the TCP/IP (Transmission Control Protocol/Internet Protocol) network protocol is used

and TCP/IP Stack software is used. The Ethernet library provided for use with the Network Shield has the necessary

stack support for using the chipKIT Max32/Network Shield in the MPIDE programming environment.

If the board is being used outside the MPIDE programming environment, the Microchip Applications Library,

available for download format www.microchip.com, provides full protocol stack support compatible with the

PIC32MX795 MAC and the LAN8720 PHY. Microchip also provides many example programs demonstrating the use

of their network protocol stack for various applications.

When not using the either the chipKIT Ethernet library or the Microchip network protocol stack, refer to the

manufacturer documentation for the PIC32MX795 and LAN8720, as well as network protocol documentation, for

information on using the Ethernet interface.

The PIC32MX795 microcontroller has 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 is designed to use the standard (not alternate) pins, and to use the RMII (not 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, which 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, 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 the NRST must be driven high

before initializing the Microchip network stack. When using the chipKIT Ethernet library for the Network Shield,

this is done automatically by the library.

Other product and company names mentioned may be trademarks of their respective owners.

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