OK
This weekend I have done some test and will share what I get with you:
Following is for Kenwood head unit with 13pin round plug older than 1999.
I don't have CD changer so I can't confirm this info, use it at your own risk.
Pin out is:
4 3 2 1
8 7 6 5
12 11 10 9
13
1 REQH OUT Request output to changer; "Low" : Request
2 GND - Ground
3 BU + 12 OUT Vcc +12V
4 CH CON OUT Changer control; "High" : Operation mode "Low" : Standby
5 CH MUTE IN Mute request from changer; "High" : Mute
6 A GND - Audio Ground
7 CH RST OUT Reset output to changer
8 R AUDIO IN Audio right channel
9 REQC IN Request input from changer; "Low" : Request
10 DATAC IN Data input from changer
11 DATAH OUT Data output to changer
12 L AUDIO IN Audio left channel
13 CH CLK I/O Clock input/output for changer
1. Start with:
CH MUTE, DATAC: low (0 V) and
REQC, CH CLK: high (+ 5 V)
then HU will look for a Changer.
Pressing [SRC] button give:
TUNER --> (CD -->) DISK (followed with NO CHANGER) --> TUNER etc.
2. Get data from HU:
When changing from TUNER to DISK: CH CON goes from low to high and REQH from high to low. Sending 8 clock pulse to HU give 1 byte followed with REQC low pulse, something like this:
RQEH -----+ +---------
+------------------------------------------+
CLKC ------+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +--------------
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
REQC ---------------------------------------------+ +------
+----+
when REQC goes low, REQH go high.
after REQC high, REQH goes low requesting to send another byte to changer, total 6 byte, BA D0 BC F3 D1 D4 .
after that HU will display NO CHANGER and no audio input if it don’t get answer form CDC.
3. Send data to HU
Sending data to HU is similar to get data, but I have no info about that. Can you help?
I have manage to fool the HU to think it has CD-changer connected, but the method is unstable and will not be published now.
4. Control PC from HU
When pressing Disk Control Button, HU request to send following 1 byte commands to changer:
Button down up
>>| F6 FE
|<< F7 FE
Disk + F0 FE
Disk - F1 FE
>|| F5 --
EJECT ?
SCAN (2) FA
RDM (3) DE
REP (4) DC
D-SCN (5) FB
M-RDM (6) F2
As commands are only 1 byte, it is simple task to control MP3 Player, WinAmp etc.
I hope this info will help someone and maybe someone can share more info.
Ken