8. The Balboa 32U4 USB interface
Our 32U4 family of boards are based on a single AVR ATmega32U4 microcontroller that runs the
user program and also handles the USB connection to the computer. The AVR has a full-speed USB
transceiver built into it and can be programmed to present almost any type of USB device interface to
the computer.
USB is an asymmetric system that consists of a single “host” connected to multiple “devices”. The host
is typically a personal computer. The ATmega32U4 can only act as a USB device, so an A-Star device
cannot be connected to other USB devices like mice and keyboards; it can only be connected to a
host such as your computer.
Programming an ATmega32U4 board using the Arduino IDE as described earlier will automatically
configure it as a composite device with a single virtual serial port. If you program the microcontroller
with an Arduino sketch that implements another USB device class, like HID or MIDI, you will see
additional child devices as well.
On a Windows computer, you can see the virtual serial port by going to your computer’s Device
Manager and expanding the “Ports (COM & LPT)” list. You should see a COM port labeled “Pololu A-
Star 32U4”. In parentheses after the name, you will see the name of the port (e.g. “COM3” or “COM4”).
Windows will assign a different COM port number to the device depending on what USB port you
plug it into and whether it is in bootloader mode or not. If you need to change the COM port number
assigned to the A-Star, you can do so using the Device Manager. Double-click on the COM port to
open its properties dialog, and click the “Advanced…” button in the “Port Settings” tab. From this dialog
you can change the COM port assigned to the device.
Windows 10 Device Manager showing the A-Star’s virtual COM port.
On a Windows computer, you can see the rest of the USB interface by going to the Device Manager,
selecting
View > Devices by connection
, and then expanding entries until you find the “Pololu A-Star
Pololu Balboa 32U4 Balancing Robot User’s Guide
© 2001–2019 Pololu Corporation
8. The Balboa 32U4 USB interface
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