Carloop Retro sounds very cool. I do think it is a K Line communication, it sounds to my uneducated brain like the same type of data as OBD only over a different connection protocol.
You may understand the attached better than I do, but I will keep the dialog going as I learn more.
ADS and the need for real serial ports.
The one question I receive frequently is “why doesn’t your interface work with a Serial to USB adapter?”
The truth is, it does work with a serial to USB adapter, BUT ONLY IN OBD MODE. Why is this?
If one looks at the history of ADS, one will find that it was designed in the good old DOS operating system and slow computers days. To eek out a modicum of speed a method was used called Direct Hardware Access [DHA]. So in case of the serial port, the software would directly talk to the computer address 0x3F8 and would listen for incoming characters by looking at Interrupt Request [IRQ] #4. IRQs are like semaphore flags, when a character is received by the computer, the flag is raised, in this case flag #4, and a program can watch for this and process the character.
So the old original software used by BMW, directly accesses a computer serial chip with the address 0X3F8 and uses IRQ 4 to show there is a character.
ADS also uses 2 lines to talk, called the K line and the L line. Which line to use is controlled by using one of the RS232 handshake lines such as DTR, etc. Strobe the handshake line high and communication is via K line and strobe it low and communications is via the L line. This is pretty well described in a document called ADS_DOCU.pdf that floats around on the internet.
USB, by definition, and in principle, did away with handshake lines, ergo, strobing, using the L line, became much more cumbersome. Now, not all modules use the L line, so, in a false sense of security, one finds that some modules talk just dandy in ADS mode, through the 20 pin ADS connector, and frustratingly, others won’t. Murphy’s Law will predict that the module u desperately want/need to talk to requires the L line to wake up.
OBD mode did away with the strobing and line switching and only uses the K line, so using a USB adapter is possible.