class USB_VCP – USB virtual comm port

The USB_VCP class allows creation of a stream-like object representing the USB virtual comm port. It can be used to read and write data over USB to the connected host.


class pyb.USB_VCP(id=0)

Create a new USB_VCP object. The id argument specifies which USB VCP port to use.

Create a new USB_VCP object.


USB_VCP.init(*, flow=-1)

Configure the USB VCP port. If the flow argument is not -1 then the value sets the flow control, which can be a bitwise-or of USB_VCP.RTS and USB_VCP.CTS. RTS is used to control read behaviour and CTS, to control write behaviour.


Set the character which interrupts running Python code. This is set to 3 (CTRL-C) by default, and when a CTRL-C character is received over the USB VCP port, a KeyboardInterrupt exception is raised.

Set to -1 to disable this interrupt feature. This is useful when you want to send raw bytes over the USB VCP port.


Return True if USB is connected as a serial device, else False.


Return True if OpenMV IDE is connected to the OpenMV Cam.


Return True if any characters waiting, else False.


This method does nothing. It exists so the USB_VCP object can act as a file.[nbytes])

Read at most nbytes from the serial device and return them as a bytes object. If nbytes is not specified then the method reads all available bytes from the serial device. USB_VCP stream implicitly works in non-blocking mode, so if no pending data available, this method will return immediately with None value.

USB_VCP.readinto(buf[, maxlen])

Read bytes from the serial device and store them into buf, which should be a buffer-like object. At most len(buf) bytes are read. If maxlen is given and then at most min(maxlen, len(buf)) bytes are read.

Returns the number of bytes read and stored into buf or None if no pending data available.


Read a whole line from the serial device.

Returns a bytes object containing the data, including the trailing newline character or None if no pending data available.


Read as much data as possible from the serial device, breaking it into lines.

Returns a list of bytes objects, each object being one of the lines. Each line will include the newline character.


Write the bytes from buf to the serial device.

Returns the number of bytes written.

USB_VCP.recv(data, *, timeout=5000)

Receive data on the bus:

  • data can be an integer, which is the number of bytes to receive, or a mutable buffer, which will be filled with received bytes.

  • timeout is the timeout in milliseconds to wait for the receive.

Return value: if data is an integer then a new buffer of the bytes received, otherwise the number of bytes read into data is returned.

USB_VCP.send(data, *, timeout=5000)

Send data over the USB VCP:

  • data is the data to send (an integer to send, or a buffer object).

  • timeout is the timeout in milliseconds to wait for the send.

Return value: number of bytes sent.

USB_VCP.irq(handler=None, trigger=IRQ_RX, hard=False)

Register handler to be called whenever an event specified by trigger occurs. The handler function must take exactly one argument, which will be the USB VCP object. Pass in None to disable the callback.

Valid values for trigger are:

  • USB_VCP.IRQ_RX: new data is available for reading from the USB VCP object.



to select the flow control type.


IRQ trigger values for USB_VCP.irq().