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chipKIT™ Network Shield™ Reference Manual

Connectors J6 and J7 can be used to extend the I

These are standard 2x4 pin header connectors with 0.100" spaced pins. They provide access to the I

and SDA, plus VCC3V3 and ground. The VCC3V3 can be used to power external I

The I

C bus uses open-collector drivers to allow multiple devices to drive the bus signals. This means that pull-up

resistors must be provided to supply the logic high state for the signals. The Network Shield provides 2.2Kohm pull-

up resistors on I

C #1. Because I

connected.

Jumpers JP9 & JP12 let I

C #1 be disconnected from the Network Shield if it is not in use but is interfering with the

associated pins. There are cuttable traces on the underside of the board between the pins of these jumpers. Cut

these traces to disconnect SCL1 and SDA1 from the Network Shield. To restore the connection, load two pin

headers for JP9 and JP12 and install shorting blocks. If this is done, it is still possible to access the on-board

EEPROM by connecting SCL and SDA from I

EEPROM will then appear on I

The logic high pull-up for I

C #2 is provided by sourcing current mirrors instead of resistors. These current mirrors

source approximately 1.7mA. The use of current mirrors provides faster rise times on the I

the ability to drive longer cable runs reliably than would be the case with simple pull-up resistors.

Generally, only one set of pull-ups is used on the bus. Jumpers JP10 and JP11 can be used to disable the on-board

pull-ups on I

C #2 if a different value is needed or some other device on the bus is providing the pull-ups or if I

isn't being used and the pull-ups are interfering with the use of the pins. The on-board pull-ups are enabled by

install shorting blocks on JP10 and JP11. Removing the shorting blocks disables the pull-ups.

Digilent has several small I/O peripheral modules (Pmods™) available that can be connected using the I

connector. These include a 3-axis accelerometer, a 4-channel 12-bit A/D converter, a serial character LCD panel, a

3-axis gyroscope, a real-time clock/calendar, and an I/O expander.

2.4.1 EEPROM

A 256Kbit (32Kbyte) I

C EEPROM is provided using a Microchip 24LC256. This EEPROM, IC5, is located on the

bottom of the board.

The EEPROM is on the I

C #1 bus, and its 7-bit I

Digilent has a library for using the EEPROM. It is contained in document # DSD-0000311 (chipKIT IOShield

Library.zip) which can be downloaded from the Basic I/O Shield product page at www.digilentinc.com. The

EEPROM library is IOShieldEEPROM.

For details on the 24LC256, see the data sheet at www.microchip.com.

2.5

32.768 KHz Oscillator

A 32.768 KHz oscillator is provided for use as a clock source for the real-time clock/calendar (RTCC) peripheral in

the PIC32MX796 microcontroller on the Max32 board. The output of this oscillator connects to pin 12 or connector

J11.

On the Max32 board, this signal connects to signal RC13, which connects to pin 73 on the PIC32 microcontroller.

This pin provides the secondary oscillator input, which can be used to clock the RTCC in the PIC32 microcontroller.

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

C busses off of the board to connect to external I

C #1 is the bus with the EEPROM, these pull-up resistors are permanently

C #2 by installing jumper wires between connector J6 and J7. The

C #2 bus.

C device address is '1010000'.

C devices.

C signals, SCL

C devices.

C signals and provides

Page 8 of 10

C #2