Handshaking... Error Unexpected Response 0x68 Jun 2026
If the basic steps fail, the issue might be deeper in your environment setup.
At first glance, 0x68 looks like just another hexadecimal byte. But to the system expecting a specific handshake sequence, receiving 0x68 is like hearing "Goodbye" when you said "Hello." This article will dissect what this error means, why it occurs across different protocols (especially in ISO 7816, T=0/T=1 protocols, M-bus, and proprietary bootloaders), and how to systematically resolve it.
If you have sensors or displays connected to GPIO0, GPIO2, or the RX/TX pins, they can interfere with the flashing process. Step-by-Step Troubleshooting Guide Follow these steps in order to resolve the 0x68 error. 1. Check the Physical Connection handshaking... error unexpected response 0x68
The error during a handshaking process is most commonly associated with Unlocktool or similar mobile servicing software when the server receives a response identifier it doesn't recognize . In the context of network protocols like HTTP/2 over TLS , the hex value 0x68 (followed by 0x32 ) specifically identifies the "h2" protocol string. Common Fixes for Unlocktool Handshaking Errors
ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=1) time.sleep(0.5) # important If the basic steps fail, the issue might
import serial, time
When getty or systemd-logind expects a specific login handshake on a serial console (e.g., from a device like a BeagleBone or Raspberry Pi Pico), and the device sends 0x68 (ASCII 'h') as garbage due to baud rate mismatch. If you have sensors or displays connected to
If you see this error, follow this structured approach:
ser.reset_input_buffer() ser.write(b'\x10\x02') timeout = time.time() + 1 while time.time() < timeout: if ser.in_waiting: first_byte = ser.read(1) if first_byte == b'\x68': # It's a data frame, not ACK. Handle it. length = ser.read(1) # often 2nd byte is length frame = ser.read(ord(length) + 2) print("Received data frame, not handshake ACK") continue # or break elif first_byte == b'\x06': print("Handshake OK") break
ser.write(b'\x7F') # bootloader sync byte resp = ser.read(1) if resp == b'\x79': print("Handshake OK") elif resp == b'\x68': print("Unexpected 0x68 – device error or wrong mode") # Try resetting device or reconfiguring ser.write(b'\x7F') # retry once time.sleep(0.1) resp2 = ser.read(1) else: print(f"Invalid response: resp.hex()")
| Context | Meaning of 0x68 | Why the error occurs | | :--- | :--- | :--- | | | Letter 'h' | A debug print, log message, or "help" command is being sent accidentally. | | Modbus RTU | Not standard. 0x68 is 104 decimal. Could be part of a slave address or data. | The master is in a different mode (e.g., expecting ASCII) but receiving RTU binary. | | Proprietary POS (Verifone, Ingenico) | Used in specific TLV (Type-Length-Value) structures. | The handshake state machine is corrupted. The device sent a data packet instead of a control byte. | | Bootloader handshake | A custom command like "Enter programming mode". | The device is not in bootloader mode; it's running application code that prints 'h' over UART. |