2.19 USB Serial Module API Manual

Overview

The USB Serial module provides functionality for data communication via USB serial ports. This module implements the standard stream protocol interface and supports read/write operations.

This module supports communication with 4G modules via AT commands.

Constructor

usb_serial(path="/dev/ttyUSB1", timeout_ms=300)

Creates a USB Serial object.

Parameters:

• path (str): Serial device path, defaults to “/dev/ttyUSB1”

• timeout_ms (int): Read/write timeout in milliseconds, defaults to 300ms

Returns: USB Serial object

Example:

import usb_serial

# Create USB Serial object
serial = usb_serial.usb_serial("/dev/ttyUSB1", timeout_ms=300)

Methods

open([path])

Opens the USB serial device.

Parameters:

• path (str, optional): If provided, will use this path instead of the one specified in the constructor

Returns:

• True: Open successful

• False: Open failed

Example:

serial.open()  # Use path specified in constructor
serial.open("/dev/ttyUSB2")  # Use new path

close()

Closes the USB serial device.

Example:

serial.close()

read(size)

Reads data from the serial port.

Parameters:

• size (int): Number of bytes to read

Returns: Read data (bytes type)

readinto(buf)

Reads data into a buffer.

Parameters:

• buf (bytearray): Target buffer

Returns: Number of bytes actually read

readline()

Reads a line of data until encountering a newline character or timeout.

Returns: Line data read (bytes type)

write(buf)

Writes data to the serial port.

Parameters:

• buf (bytes/bytearray): Data to write

Returns: Number of bytes actually written

Properties

path

Gets or sets the serial device path.

Example:

print(serial.path)  # Get current path
serial.path = "/dev/ttyUSB1"  # Set new path

timeout_ms

Gets or sets the read/write timeout (milliseconds).

Example:

print(serial.timeout_ms)  # Get current timeout
serial.timeout_ms = 1000  # Set timeout to 1 second

Stream Protocol Support

The USB Serial object implements the standard stream protocol and can be directly used in contexts requiring stream objects.

Example:

# Read a line of data using readline()
line = serial.readline()

# Write data using write()
serial.write(b"Hello World\n")

Notes

1. The close() method is automatically called when the object is destroyed

2. All read/write operations are controlled by the timeout_ms parameter

3. Calling read/write methods when the serial port is not open will raise an OSError exception

4. The default device path is “/dev/ttyUSB1” - please modify according to actual device