Digilent chipKIT Network Shield Справочное руководство и руководство пользователя - Страница 8

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chipKIT Network Shield Reference Manual

The CAN network standard requires that the

nodes at each end of a network provide 120

ohm termination. The Network Shield provides

the termination resistors and jumpers to

enable/disable them depending on the location

of the board in the network. Jumper JP6 is

used to enable/disable the termination resistor

for the CAN1 network, and JP8 is used to

enable/disable the termination resistor for

CAN2. Install a shorting block on the jumper

pins to enable the termination resistor, or

remove the shorting block to disable the

termination resistor.

C Busses and Connectors

The Inter-Integrated Circuit (I

provides a medium speed (100K or 400K bps)

synchronous serial communications bus. The

C interface provides master and slave

operation using either 7 bit or 10 bit device

addressing. Each device is given a unique

address, and the protocol provides the ability

to address packets to a specific device or to

broadcast packets to all devices on the bus.

Refer to the Microchip PIC32MX7XX Data

Sheet and the PIC32 Family Reference

Manual for detailed information on configuring

and using the I

C interface.

The PIC32MX795 microcontroller on the

Max32 provides for up to five independent I

interfaces. The Network Shield is designed to

provide access to two of these interfaces I

#1 (SCL1, SDA1) and I

I2C #1 is the bus accessed through the

standard chipKIT Wire library. There are two

sets of connectors on the board for access to

the two I

C ports. Connector J7 provides

access to I

C port #1 while connector J6

provides access to I

C port #2.

The user should note that external interrupt 3

and SCL1 share the same pin on the

PIC32MX795. External interrupt 4 and SDA1

also share the same pin. Therefore, external

interrupts 3 and 4 should not be used

simultaneously with I2C bus #1.

www.digilentinc.com

) Interface

C #2 (SCL2, SDA2).

One I

C device is provided on the Network

Shield. This is a 256Kbit EEPROM connected

to the I

C #1 bus.

C Connectors: Connectors J6 and J7 can be

used to extend the I

C busses off of the board

to connect to external I

standard 2x4 pin header connectors with

0.100" spaced pins. They provide access to

the I

C signals, SCL and SDA, plus VCC3V3

and ground. The VCC3V3 can be used to

power external I

C devices.

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. As I

with the EEPROM, these pull-up resistors are

permanently connected.

Jumpers JP9 & JP12 are provided to allow I

#1 to be disconnected from the Network

Shield, if it not being used and is interfering

with the use of the associated pins. There are

cut-able 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

installing jumper wires between connector J6

and J7. The EEPROM will then appear on I

bus #2.

The logic high pull-up for I

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

provides 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 are used on

the bus. Jumpers JP10 and JP11 can be used

to disable the on-board pull-ups on I

C devices. These are

C #1 is the bus

C #2 by

C #2 is provided by

C signals and

C #2 if a

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