Handshaking... Error Unexpected Response 0x68 [Tested ✔]

An engineer tries to read an ISKRA MT382 meter using M-Bus over 300 baud. Error: handshaking... error unexpected response 0x68 .

: The value 0x68 is the first byte of the ALPN protocol identifier for HTTP/2 ( h2 ). If a client expecting a standard TLS handshake receives this instead, it may trigger an "unexpected response" error. handshaking... error unexpected response 0x68

The modem may be busy with a background task (like searching for a network) and rejects the handshake. 💡 Troubleshooting Steps Phase 1: Physical & Power Voltage Check: An engineer tries to read an ISKRA MT382

ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=1) time.sleep(0.5) # important : The value 0x68 is the first byte

If you control the device firmware, add debug UART to print the received byte before sending 0x68 . You might discover the host sent 0x68 instead of the expected command!

In the world of serial communication, industrial automation, and firmware development, few things are as frustrating as a cryptic handshake error. Among these, the error message is a notorious roadblock. It typically appears during device initialization, firmware updates, or data exchange between a host (PC, microcontroller) and a peripheral device (printer, sensor, smart meter, payment terminal, or bootloader).

: The 0x68 error can occur if your ISP is blocking the server response. Try connecting through a VPN to change your routing path.