Handshaking... Error Unexpected Response 0x68 May 2026

Embedded devices often enter a bootloader on startup, expecting a specific "magic byte" sequence (e.g., 0x7F for STM32, or 0x55 for Arduino). If the host sends the wrong byte due to a script error, the bootloader might reply with an error code.

A $20 USB logic analyzer (Saleae clone) will end all guesswork. Probe the RX and TX lines. Look for: handshaking... error unexpected response 0x68

import serial, time
ser = serial.Serial(
port='/dev/ttyUSB0',
baudrate=9600,
bytesize=8,
parity='N',  # or 'E' for even
stopbits=1,
timeout=2
) Embedded devices often enter a bootloader on startup,
If you are testing the module on a breadboard or with loose jumper wires: 0x7F  for STM32