User Manual

Cerebot 32MX7 Reference Manual
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The RJ45 connector J11, provides the physical
connection to an Ethernet network using a
standard Ethernet cable.
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 Cerebot 32MX7 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 operate with 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
must be used. The Microchip Applications
Library, available for download from the
Microchip web site provides full protocol stack
support compatible with the PIC32MX795 MAC
and the LAN8720 PHY. Microchip also
provides numerous example programs
illustrating the use of their network protocol
stack for various applications.
When not using the Microchip network protocol
stack, refer to the manufacturer documentation
for the PIC32MX795 and LAN8720, plus
network 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 Cerebot
32MX7 is 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 LAN8720 PHY has a reset signal, labeled
NRST in the schematic, that can be used to
reset the PHY. This signal is connected to the
INT2/RE9 pin on the PIC32 microcontroller.
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 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.
CAN Interfaces
The Controller Area Network (CAN) standard is
a control networking standard originally
developed for use in automobile systems, but
has since become a standard used in various
industrial control and building automation
networking applications as well.
The PIC32MX795 microcontroller contains two
independent CAN network controllers. These
CAN controllers in combination with two
Microchip MCP2551 CAN transceivers allow
the Cerebot 32MX7 board to operate on up to
two independent CAN networks. Refer to the
PIC32MX7XX data sheet and the PIC32
Family Reference Manual, plus CAN network
documentation for information on operation of
the CAN controllers and CAN networking in
general.