Open and uninstall existing MTK or Preloader drivers.

Using a logic analyzer, engineers discovered that the PLC’s firmware delayed its response by 500ms on some cold starts, but the PC’s timeout was 200ms. After the timeout, the PC sent a reset command. However, the PLC responded with 0x68 as part of its startup diagnostic output. The PC interpreted this diagnostic byte as a handshake reply.

Crucially, this error message is not a standardized code that means the same thing everywhere. Its interpretation depends heavily on the specific protocol and system in use. In essence, it's the device's way of saying, "I received 0x68 , but I was looking for something else entirely." This could mean the slave device is faulty, the communication parameters are mismatched, a different protocol is in use, or even that a completely correct but unrecognized command was issued.

If you receive an unexpected byte (like 0x68 ), don’t fail immediately. Instead: