Do you want to communicate with the CD Changer by emulating the head unit?
If so this has also already been been done here where they have emulated both the head unit and the CD Changer:
VAG CD Changer Simulator
VAG/Panasonic CD Changer Remote Control
I still don't understand what you are trying to do. What does "removing MP3 CD DRIVE" mean? What is the "MP3 CD DRIVE"? Is it the headunit or a seperate device connected to he headunit? OR maybe just a part inside the headunit?
How do you expect to get help when you don't post the source code or schematic?
But wouldn't it be better toask for hel in a PIC BASIC forum (if that's what you use)?
here is the 2DIN AUDI concert III
It is a radio unit with MP3 capabilities (there is a CD DRIVE inside which read MP3's)
Is it clearer?
I would like to remove it and replace it by an adapter which will emulate PC playlist (Winamp, WMplayer, Centrafuse) to a virtual MP3 CD.
There must be a 2-way communication between the drive and the PCB. Maybe you are missing one of the SPI lines? Or maybe the data line is bi-directional?
What en generates the measure enale, cloc and data? The PCB or drive or maybe some lines aregenerated in one end and others in the orther end.
This project was in stand by. I decided to continue it before being father to the end of march....
This doesn't let me a lot of time....
Added Picture of the AUDI CONCERT III MP3 CD DRIVE BP7-VA to first post