Ethernet Interface - Digilent chipKIT Pro MX7 Reference Manual

chipKIT™ Pro MX7 Board Reference Manual
Using the internal system clock phase-locked loop (PLL), it is possible to select numerous multiples or divisions of
the 8 MHz oscillator to produce CPU operating frequencies up to 80 MHz. The clock circuit PLL provides an input
divider, multiplier, and output divider. The external clock frequency (8 MHz) is first divided by the input divider
value selected. This is multiplied by the selected multiplier value and then finally divided by the selected output
divider. The result is the system clock, SYSCLK, frequency. The SYSCLK frequency is used by the CPU, DMA
controller, interrupt controller, and pre-fetch cache.
The operating frequency is selected using the PIC32MX795 configuration variables. These are set using the
#pragma config statement. Use #pragma config FPLLIDIV to set the input divider, #pragma
config FPLLMUL to set the multiplication factor, and #pragma config FPLLODIV to set the output
divider. Refer to the PIC32MX5XX/6XX/7XX Family Data Sheet and the PIC32MX Family Reference Manual, Section
6 Oscillators for information on how to choose the correct values, as not all combinations of multiplication and
division factors will work.
In addition to configuring the SYSCLK frequency, the peripheral bus clock, PBCLK, frequency is also configurable.
The peripheral bus clock is used for most peripheral devices, and in particular is the clock used by the timers and
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serial controllers (UART, SPI, I C). The PBLCK frequency is a division of the SYSCLK frequency selected using
#pragma config FPBDIV. The PBCLK divider can be set to divide by 1, 2, 4, or 8.
The following example will set up the chipKIT Pro MX7 for operation with a SYSCLK frequency of 80 MHz and a
PBCLK frequency of 10 MHz:
#pragma config FNOSC = PRIPLL
#pragma config POSCMOD = EC
#pragma config FPLLIDIV = DIV_2
#pragma config FPLLMUL = MUL_20
#pragma config FPLLODIV = DIV_1
#pragma config FPBDIV = DIV_8
Documentation for the PIC32 configuration variables can be found in the PIC32MX Configuration Settings guide.
This is found using the "Help.Topics..." command in the MPLAB IDE. Also, refer to Appendix C for an example of
setting the configuration variables.
When using the chipKIT Pro MX7 with the MPIDE software, the clock source is set by the boot loader and no action
is required.
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Ethernet Interface

The chipKIT Pro MX7 provides the ability to interface with 10Mbps or 100Mbps Ethernet networks. The
PIC32MX795 microcontroller contains a 10/100 Ethernet Medium Access Controller (MAC). External to the PIC32
microcontroller, the chipKIT Pro MX7 board provides an SMSC LAN8720 Ethernet Physical Layer Transceiver (PHY).
Together, the MAC and PHY in combination with an appropriate coupling transformer and RJ45 jack provide a
standard 10/100 Ethernet interface.
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. Each
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