Digilent chipKIT Network Shield Справочное руководство - Страница 6
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Печатать страницуchipKIT™ Network Shield™ Reference Manual
Jumper JP4 on the Network Shield is used to route power to the host connector being used. Place the shorting
block in the "A" position when using the standard USB type-A (host) connector J4. Place the shorting block in the
"MICRO" position for use with the USB micro-AB (OTG) connector J2.
When operating as a USB host, the PIC32MX795 microcontroller controls application of power to the connected
device via the VBUSON control pin (labeled VBUSON in the schematic). Bus power is applied to the USB bus by
driving the VBUSON pin high. Power is removed from the bus by driving the VBUSON pin low. The VBUSON pin is
accessed via bit 3 of the U1OTGCON register. The VBUSON signal is shared with same microcontroller pin as analog
input A5 and digital pin 59.
The VBUSON pin drives the enable input of a TPS2051B current-limited power distribution switch to control the
application of USB power to the host connector. This switch has over-current detection capability and provides an
over-current fault indication by pulling the signal USBOC low. The over-current output pin can be monitored via
the INT1/RE8 pin on the PIC32MX795 microcontroller. This signal appears on connector J14, pin 5 on the Max32
board, and chipKIT digital pin 2. Details about the TPS2051B are available from the data sheet at the Texas
Instruments web site.
The VBUSON signal is shared with the same microcontroller pin as analog input A5 and digital pin 59. This pin is not
available for other uses when operating as a USB host. If the Max32/Network Shield is not being used as a USB
host, you can use A5/pin 59 by cutting the trace on the bottom of JP3. USB host capability can be restored by
soldering a 2-pin header to JP3 and installing a shorting block.
The PIC32 USB controller can be accessed using the chipKIT USB libraries for use within the MPIDE environment.
When using the Max32/Network Shield outside the MPIDE environment, the Microchip Application Library
provides USB stack code that can be used with the Max32/Network Shield. There are reference designs available
on the Microchip web site demonstrating both device and host operation of PIC32 microcontrollers. These
reference designs are suitable for developing USB firmware for the Max32/Network Shield.
2.3
CAN Interface
The Controller Area Network (CAN) is a control networking standard originally developed for use in automotive
systems, but has since become a standard used in various industrial control and building automation networking
applications as well.
The PIC32MX795 microcontroller on the Max32 contains two independent CAN network controllers. These CAN
controllers in combination with two Microchip MCP2551 CAN transceivers on the Network Shield allow the
Max32/Network Shield to operate on one or two independent CAN networks.
When not using the MPIDE environment, refer to the PIC32MX7XX data sheet, the PIC32 Family Reference Manual,
and the CAN network documentation available at www.microchip.com for information on CAN controllers and
CAN networking in general.
The PIC32MX795 microcontroller provides two sets of pins that can be used to connect the CAN controllers to the
external transceivers. The Max32/Network Shield is designed to use the alternate (not the standard) pins. This
selection is made using the configuration variables in the microcontroller, set using a #pragma config
statement. To select the use of the alternate interface pins, the following statement must appear in the main
program module:
#pragma config FCANIO=OFF
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