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Introduction[edit | edit source]

The Universal Serial Bus protocol is used to connect many different devices to a computer, such as keyboards, mice, CD readers, video cameras and audio ports.

Hardware view[edit | edit source]

The Mizar32 has a micro OTG (On-The-Go) USB socket which can act as a USB device to be seen by an external computer, or as a USB master to talk with USB devices.

Software view[edit | edit source]

You can't program the USB subsystem directly from Hempl. Instead, it contains software that pretends to be a USB serial port which is connected to the Hempl console in the SimpleMachines firmware releases from 2013 onwards (before that, the console was connected to a real serial port on the Mizar32 RS232 UART add-on hardware module.)

On a GNU/Linux PC, you can use the minicom terminal to talk to Hempl's USB serial port, specifying the serial device as /dev/ttyACM0. When it's talking to a GNU/Linux-based operating system it takes about 8 seconds for the Mizar32 and the PC to start talking to one another after you power the Mizar32 on.

On Windows it should appear as a USB serial device when you plug it in and you can use the PuTTY terminal emulator to talk to it but the whole system hangs if you reset or power-cycle the Mizar32. To get the Mizar32 and Windows talking to each other again, a Windows user writes:

"In Win, for the USB CDC to be recognised, you must disconnect it from
Mizar32, close the terminal ["putty"], reconnect Mizar32, reopen the
If you press Reset on the Mizar32, you must disconnect the Mizar32
from the usb, close the terminal, reconnect the Mizar32, re-open the

As used by the DFU boot loader[edit | edit source]

When the Device Firmware Upgrade Boot Loader software is activated, it also uses the USB port to talk to your PC, but not as a USB serial port. Instead, it emulates a special Atmel device which speaks the DFU firmware-updating language and requires special software on the attached PC, such as dfu-programmer or batchisp3. See the Advanced Topic on flashing firmware to the Mizar32 with the DFU bootloader.