Another frequent culprit is a hardware flow control (handshaking) mismatch. If one device expects hardware handshaking using RTS/CTS lines, and the other has it disabled or uses different pins, communication will fail. The receiving device may interpret noise or line state changes as data, resulting in a 0x68 appearing at an unexpected time. This can also occur with software XON/XOFF flow control if the devices are not configured identically.
In networking, a "handshake" is the initial negotiation where two devices agree on how to communicate securely (using SSL/TLS protocols
The 0x68 byte is frequently triggered by a sudden drop in voltage during the switch from a device's charging mode to its flashing state. handshaking error unexpected response 0x68
He typed: HANDSHAKE ACCEPTED.
: Confirm the device is actually in "bootloader mode" (often triggered by holding a button during startup). If the device is running its normal firmware, it might send data that the programmer interprets as an error. Another frequent culprit is a hardware flow control
Use a logic analyzer (Saleae, USBee) or a second PC with a serial sniffer (Termite, RealTerm, or socat on Linux). Connect the analyzer to the TX/RX lines simultaneously . Verify:
In custom embedded systems, the value 0x68 might be entirely user-defined. For example, in some touchscreen or HID (Human Interface Device) protocols, a data packet starting with 0x68 is used by a device to report touch events when it is in a low-power sleep mode. In this scenario, receiving 0x68 is not an error at all; it's a valid data report. The "handshaking error" would then occur because the host's firmware was not designed to recognize this report as part of the handshake sequence. It expected a specific acknowledgment byte, but the slave device, perhaps still in sleep mode, sent a touch event packet starting with 0x68 instead. This can also occur with software XON/XOFF flow
The device is not in the correct BROM mode or the bootloader is locked.
Trying to access a secure ( HTTPS ) endpoint via a non-secure ( HTTP ) port (or vice versa) can lead to "unexpected packet format" errors. Recommended Troubleshooting Steps