I was given this chinese OBD2 adapter which came with a disc that contained a suspicious cracked copy of VCDS. Those adapters usually only work with the exact copy that is on the disc. Since the adapters are usually nothing special and are just back to back adapters to get from USB to OBD I was interested in seeing how exactly it works with the intention to get it running on a more recent version of VCDS.

• Chips on adapter:
  ATMEGA162 - Microcontroller
  STC12C2052AD - secondary Microcontroller (security chip)
  ATF16V8B - Atmel PLC
  FT232RL - USB to UART adapter
  TJA1050 - CAN Transceiver IC
  MCP2515 - CAN Protocol IC

• Connection chain:

  computer to ATMEGA -USB-> FTDI FT232RL -UART-> ATMEGA162

  ATMEGA to car -SPI-> MCP2515 -> TJA1050 -CAN-> Car

  //todo: missing is the PLC and what exactly it does here

The good thing about this adapter is that it uses genuine hardware. What is interesting is the STC chip that seems to be another chip not directly related with communicating with the car.

Digging through some forums and a few failed attempts trying to flash the ATMEGA, the purpose of this chip became clear: Running unpatched VCDS software will wipe the firmware of your adapter if it finds out that it is non-genuine hardware. This STC chip prevents the device being flashed/reflashing the modded chinese firmware back.

Simply removing the STC chip¹ with a hot air gun made the ATMEGA flashable again and I was able to install my desired firmware to it.

I setup a clean Windows VM, passed the adapter through, downloaded an original copy of VCDS 22.10 (x86) and Kolimer patches² for it.

STC Chip¹: https://mhhauto.com/Thread-VCDS-VAG-COM-REPAIR?page=137
VCDS/Kolimer²: https://sidicer.lt/vcds/