7. The Zumo 32U4 USB interface
The A-Star and Zumo 32U4 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 and a human interface device (HID) with a keyboard
and mouse. Since we preload an example Arduino sketch on each device before it ships, this is the default USB
configuration of the device.
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 8 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 32U4” COM port.
Near it, you should see the parent composite device and the human interface device.
Pololu Zumo 32U4 Robot User’s Guide
© 2001–2015 Pololu Corporation
7. The Zumo 32U4 USB interface
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