It's easy to use the RS232 Pal with Python or CircuitPython, and the built-in UART module. This module allows you to easily write Python code to send and receive UART messages.

You can use this driver with any CircuitPython microcontroller board or with a computer that has GPIO, UART and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility library. For Blinka, this example was tested with a Raspberry Pi. To use the example as-is with built-in UART, you'll need to follow these configuration steps outlined in the Blinka Learn Guide.

You'll need an external RS-232 device to use this example with the breakout:

CircuitPython Microcontroller Wiring

First, wire up the RS-232 connection to the RS232 Pal exactly as follows. Then, wire up the RS232 Pal to your board. The following is the breakout wired to a Feather RP2040 and RS-232 connection:

The following is the breakout wired to a Feather RP2040 and RS-232 connection using a solderless breadboard:

Python Computer Wiring

Since there are dozens of Linux computers/boards you can use, we will show wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported.

Here's the Raspberry Pi wired to the RS232 Pal and RS-232 connection:

Here's the Raspberry Pi wired up using a solderless breadboard:

CircuitPython Usage

To use with CircuitPython, you'll need to update code.py with the example script.

Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, and copy the code.py file to your CIRCUITPY drive.

There are no additional libraries needed for this example. All of the modules used are built-in.

Python Usage

Once you have the library pip3 installed on your computer, copy or download the following example to your computer, and run the following, replacing code.py with whatever you named the file:

python3 code.py

Example Code

If running CircuitPython: Once everything is saved to the CIRCUITPY drive, connect to the serial console to see the data printed out!

If running Python: The console output will appear wherever you are running Python.

# SPDX-FileCopyrightText: 2024 Liz Clark for Adafruit Industries
# SPDX-License-Identifier: MIT

import time
import board

# baud rate for your device
baud = 38400
# Initialize UART for the CH9328
# check for Raspberry Pi
# pylint: disable=simplifiable-condition
if "CE0" and "CE1" in dir(board):
    import serial

    uart = serial.Serial("/dev/ttyS0", baudrate=baud, timeout=3000)
# otherwise use busio
else:
    import busio

    uart = busio.UART(board.TX, board.RX, baudrate=baud)

print("Enter commands to send to the RS-232 device. Press Ctrl+C to exit.")
while True:
    user_input = input("Please enter your command: ").strip()
    if user_input:
        # send the command with a telnet newline (CR + LF)
        uart.write((user_input + "\r\n").encode('ascii'))

    # empty buffer to collect the incoming data
    response_buffer = bytearray()

    # check for data
    time.sleep(1)
    while uart.in_waiting:
        data = uart.read(uart.in_waiting)
        if data:
            response_buffer.extend(data)

    # decode and print
    if response_buffer:
        print(response_buffer.decode('ascii'), end='')
        print()

# SPDX-FileCopyrightText: 2024 Liz Clark for Adafruit Industries
# SPDX-License-Identifier: MIT

import time
import board

# baud rate for your device
baud = 38400
# Initialize UART for the CH9328
# check for Raspberry Pi
# pylint: disable=simplifiable-condition
if "CE0" and "CE1" in dir(board):
    import serial

    uart = serial.Serial("/dev/ttyS0", baudrate=baud, timeout=3000)
# otherwise use busio
else:
    import busio

    uart = busio.UART(board.TX, board.RX, baudrate=baud)

print("Enter commands to send to the RS-232 device. Press Ctrl+C to exit.")
while True:
    user_input = input("Please enter your command: ").strip()
    if user_input:
        # send the command with a telnet newline (CR + LF)
        uart.write((user_input + "\r\n").encode('ascii'))

    # empty buffer to collect the incoming data
    response_buffer = bytearray()

    # check for data
    time.sleep(1)
    while uart.in_waiting:
        data = uart.read(uart.in_waiting)
        if data:
            response_buffer.extend(data)

    # decode and print
    if response_buffer:
        print(response_buffer.decode('ascii'), end='')
        print()

The code begins by initializing the UART port. There is a check for a Raspberry Pi single board computer. If a Raspberry Pi is detected, then serial is used instead of busio for UART over GPIO. The baud rate for your RS-232 device is defined with baud. Edit this value to match your RS-232 device.

# baud rate for your device
baud = 38400

# baud rate for your device
baud = 38400

In the loop, the code waits for user input in the serial console. If any incoming data is received from the RS-232 device, it is printed to the serial console.

The commands that you send will vary by the RS-232 device that you connect to the RS232 Pal. The output below was sent to a StarTech HDMI switcher. The AVI=n commands switch the selected HDMI port and the VS command gives a current status of the device.