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Documentation Index

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The VESC firmware exposes a USB CDC (Communications Device Class) serial interface. This lets a host computer communicate with the VESC using the same serial packet protocol used over UART, without any additional drivers on most operating systems.

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How it works

When you plug a VESC into a computer via USB, it enumerates as a virtual serial port (CDC ACM device). The operating system assigns it a port name such as /dev/ttyACM0 on Linux, /dev/cu.usbmodem* on macOS, or COMx on Windows. VESC Tool detects this port and connects to it automatically. All configuration, motor control, real-time data display, and firmware updates flow through this interface. The USB interface is implemented in comm/comm_usb.c and exposes the following API: 
// Initialize the USB CDC interface
void comm_usb_init(void);

// Send a framed packet over USB
void comm_usb_send_packet(unsigned char *data, unsigned int len);

// Returns the number of write timeouts that have occurred
unsigned int comm_usb_get_write_timeout_cnt(void);

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Connecting with VESC Tool

1

Connect the VESC via USB

Plug the VESC into your computer using a USB cable. The device should enumerate as a virtual serial port.
2

Open VESC Tool

Launch VESC Tool. It will scan for connected devices and list available serial ports.
3

Select the port and connect

Choose the port that corresponds to your VESC and click Connect. VESC Tool will read the firmware version and device configuration automatically.

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Connection settings

Because USB CDC is a virtual serial port, there is no physical baud rate — data is transferred at USB full-speed (12 Mbit/s). Any baud rate selected in a serial terminal application is ignored by the device.
If you are connecting with a generic serial terminal instead of VESC Tool, you still need to select a baud rate in your terminal application. The value does not affect communication speed, but 115200 is a conventional default.

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Protocol over USB

The VESC USB interface uses the same framed serial protocol as UART. Bytes received from the host are fed through the packet layer (comm/packet.c), which handles framing, length, and CRC validation before passing complete packets to commands_process_packet. See the UART protocol page for the full packet format and command reference.

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Troubleshooting

  • On Linux, ensure your user is in the dialout group: sudo usermod -aG dialout $USER (requires re-login).
  • On Windows, install the STM32 Virtual COM Port driver if the device does not enumerate automatically.
  • Try a different USB cable — some cables are power-only and carry no data.
  • Verify no other application (e.g., a serial terminal) is holding the port open.
  • Disconnect and reconnect the USB cable, then try again.
  • Check App Settings -> General -> CAN Mode is not set to a mode that interferes with USB communication.
A non-zero write timeout count indicates the host is not reading data fast enough. This can happen if VESC Tool is paused or closed while the firmware is actively sending data. Reconnecting clears the condition.