Digilent chipKIT Uno32 Podręcznik referencyjny - Strona 7
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chipKIT Uno32 Hardware Description
MPIDE and USB Serial Communications
The Uno32 board is designed to be used with
the Multi-Platform IDE (MPIDE). Digilent
produced the MPIDE development platform by
modifying the Arduino™ IDE. It is backwards-
compatible with the Arduino IDE.
The MPIDE uses a serial communications port
to communicate with a boot loader running on
the Uno32 board. The serial port on the Uno32
board is implemented using an FTDI FT232R
USB serial converter. Before attempting to use
the MPIDE to communicate with the Uno32,
the appropriate USB device driver must be
installed.
The Uno32 board uses a standard mini-USB
connector for connection to a USB port on the
PC.
When the MPIDE needs to communicate with
the Uno32 board, the board is reset and starts
running the boot loader. The MPIDE then
establishes communications with the boot
loader and downloads the program to the
board.
When the MPIDE opens the serial
communications connection on the PC, the
DTR pin on the FT232R chip is driven low.
This pin is coupled through a capacitor to the
MCLR pin on the PIC32 microcontroller.
Driving the MCLR line low resets the
microcontroller, restarting execution with the
boot loader.
This automatic reset action (when the serial
communications connection is opened) can be
disabled. To disable this operation, there is a
cut-able trace on the bottom of the board
between the pins on JP1. JP1 is normally not
loaded. If the trace between the pins on JP1
has been cut, the automatic reset operation
can be restored by loading JP1 and inserting a
shorting block across it.
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Two red LEDs (LD1 and LD2) will blink when
data is being sent or received between the
Uno32 and the PC over the serial connection.
The header connector J3 provides access to
the other serial handshaking signals provided
by the FT232R. Connector J3 is not loaded at
the factory and can be installed by the user to
access these signals.
Power Supply
The Uno32 is designed to be powered either
via USB or from an external power supply.
There is an automatic switch-over circuit that
causes the external supply to be used if both
supplies are present.
The power supply section in the Uno32 uses
two voltage regulators. The first regulates the
external voltage to 5V to power the VCC5V0
bus. The second regulates the VCC5V0 bus to
3.3V to provide power to the VCC3V3 bus that
powers the PIC32 microcontroller.
The 5V voltage regulator is normally an
NCP1117. The board is designed to be able to
also use an LM1117, but the NCP1117 is the
part normally used. The NCP1117 is rated for
an output current of 1A (the LM1117 is rated
for 800mA). The dropout voltage of the
NCP1117 is a maximum of 1.2V at the rated
output current (1.3V for the LM1117).
There is a reverse polarity protection diode in
the external power supply circuit. Considering
the diode drop plus the forward drop across
the regulator, the minimum input voltage to the
regulator should be 7V to produce a reliable 5V
output. The absolute maximum input voltage of
both the NCP1117 and the LM1117 is 20V.
The recommended maximum operating
voltage is 15V.
For input voltages above 9V, the regulator will
get extremely hot when drawing high currents.
Both the NCP1117 and the LM1117 have
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