Digilent Max32 Справочное руководство - Страница 7

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Max32™ Board Reference Manual

Switch-over from USB power to external power is done automatically and the external supply will be used if both

are present.

Jumper JP1 is used to route the external power supply voltage through the on-board 5V regulator or directly to the

VCC5V0 bus, bypassing the on-board 5V regulator. Normally, JP1 is in the REG position. This routes the external

supply through the 5V regulator. Operation from an externally regulated 5V supply is provided by placing the

jumper in the BYP position.

The forward drop across the MCP1725 is typically 210mV (350mV max) at 500mA output. With JP1 in the BYP

position, this will allow correct operation of the 3.3V power supply from an input voltage down to 3.5V. This lets

you power the board from batteries and other lower voltage power sources. In that case, the VCC5V0 power bus

will not be powered at 5V.

Note: When JP2 is in the BYP position, do not apply more than 6V to the external power input. It can destroy the

3.3V regulator and possibly the PIC32 microcontroller as well.

The PIC32 microcontroller is rated to use a maximum of 98mA of current when operating at 80 MHz. This allows up

to ~400mA from the VCC3V3 bus and up to 700mA from the VCC5V0 bus to power external devices.

The POWER connector J10 is used to provide power to shields connected to the Max32 board. The following pins

are provided on this connector:

NC (pin 1): This pin is not used.

IOREF (pin 2): Provides a 3.3V reference voltage to the shield which the shield should observe as the maximum

input pin voltage to the Max32.

P32_MCLR (pin 3): This connects to the MCLR pin on the PIC32 microcontroller and can be used to reset the

PIC32.

VCC3V3 (pin 4): This routes the 3.3V power bus to shields. This pin can provide ~400mA.

VCC5V0 (pin 5): This routes the 5V power bus to shields. This pin can provide up to ~700mA to shields, however

the total provided by pins 2 and 3 shouldn't exceed 800mA.

GND (pin 6, 7): This provides a common ground connection between the Max32 and the shields.

VIN (pin 8): This connects to the voltage provided at the external power supply connector. This can be used to

provide unregulated input power to the shield. It can also be used to power the Max32 board from the shield

instead of from the external power connector.

3. 3 5V Compatibility

The PIC32 microcontroller operates at 3.3V. The original Arduino boards operate at 5V, as do many Arduino

shields.

There are two issues to consider when dealing with 5V compatibility for 3.3V logic. The first is protection of 3.3V

inputs from damage caused by 5V signals. The second is whether the 3.3V output is high enough to be recognized

as a logic high value by a 5V input.

The digital I/O pins on the PIC32 microcontroller are 5V tolerant. The analog capable I/O pins are not 5V tolerant.

To provide 5V tolerance on those pins, the Max32 contains clamp diodes and current-limiting resistors to protect

them from 5V input voltages.

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