Perform a hard factory reset of your control board using the physical reset button.

In the world of ISO 7816-4 APDU commands, the status word 68XX (where XX is a second byte providing more detail) is a specific indicator of a problem. According to older specifications, the range 68XX indicates that the "functions in CLA not supported," meaning the command's Class (CLA) byte was invalid or not supported by the card. A more modern interpretation, found within the NIST Biometric Evaluation Framework, defines CHECK_ERR_CLA_FUNCTION as 0x68 . If you receive an APDU response with SW1 = 0x68 , it signifies a problem with the command's CLA byte.

How to Fix the "Handshaking Error Unexpected Response 0x68" The is a critical connection failure that occurs when servicing, flashing, or bypassing FRP (Factory Reset Protection) on MediaTek (MTK) Android devices. It typically surfaces while using specialized utility tools like UnlockTool or open-source scripts like mtkclient on GitHub .

// Instead of expecting a single perfect byte: uint8_t handshake() uint8_t response; unsigned long timeout = millis() + 1000; // 1 second timeout while (millis() < timeout) if (Serial.available()) response == 0x15) return response; // Good ACK or NAK

can feel like hitting a brick wall in your development or networking workflow. While "0x68" (hex for 104) is a somewhat generic error code often related to connection resets or mismatched protocols,

// Later, another part of the application (or a different app) accesses the card. // The card might have been reset in the meantime.

: 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.

Reconnect and power on the devices to clear hardware memory buffers. Conclusion

When faced with a "handshaking error unexpected response 0x68," a methodical approach is far more effective than random experimentation. The following flowchart provides a roadmap for diagnosis, followed by detailed explanations of each step.

Check the pins inside the connectors for bent metal, dust, or debris.

else // Unexpected byte, flush and return error return 0xFF;