CDC Protocols

This page contains informations, links and descriptions about various CD
changer protocols.
Choose your brand:

Blaupunkt ( DMS ?? )

Here some source code for controlling a Blaupunkt car radio.

Blaupunkt DMS Sourcecodes
Blaupunkt DMS Sourcecodes
28.9 KB

It is basically a 2 wire (rx/tx) async. serial protocol with 9 bits of data
where the 8th bit is used for synchronisation.

That made it easy to interface it to a player or PC because you can use the
serial port.

The only documents that’re left is one sheet of paper containing the initial
communication between a cd changer and the radio and

the source code.

Here is the protocol cut:

baudrate 4800
0x17B (3 times ) -> no response
0x17C (3 times ) -> no response
0x17D (3 times ) -> no response
0x17E (3 times ) -> no response
0x17F (3 times ) -> no response
0x180 -> 0x180
0x48 -> 0x48
0x02 -> 0x02
0x14F ->, change in baudrate to 9600 no response
0x180 -> 0x180
0x9F -> 0x9F
0x14F -> no response
0x180 -> 0x180
0xA1 -> 0xA1
0x14F -> no response
0x180 -> 0x180
0xAD -> 0xAD
0x14F -> no response
0x180 -> 0x180
0x48 -> 0x48
0x01 -> 0x01
0x14F -> no response
0x10F <- 0x10F
0x48 <- 0x48
0x01 <- 0x01
0x14F <- 0x14F
0x103 <- 0x103
0x20 <- 0x20
0x09 <- 0x09
0x20 <- 0x20
0x00 <- 0x00
0x14F <- 0x14F
0x10B <-( text info ??? ) 0x10B
0x20 <- (8 times space ) 0x20
0x14F <- 0x14F
0x101 <-( disc / track info ??? ) 0x101
0x09 <- 0x09
0x01 <- 0x01
0x14F <- 0x14F
0x10D <- ( disc / track / time info ( BCD ) ?? ) 0x10D
0x01 <- 0x01
0x09 <- 0x09
0x43 <- 0x43
0x57 <- 0x57
0x14F <- 0x14F


Recommended links:

Patrick Loef’s Page with AVR
based Kenwood CD changer emulator (KECANI)

The protocoll used here is a synchron serial protocoll.

First let us start with the connector pinout.

The pins have a 2.54mm distance, so you can simply build a plug using some
prototyping board ………

New connector pin-out (for head units >’99?) Thanks to Patrick Loef for this

pin direction description
1 O CH-REQH – Request output to changer; “Low” : Request
2 Ground
3 Vcc +12V
4 O CH-CON – Changer control; “High” : Operation mode “Low”
: Standby
5 I CH-MUTE – Mute request from changer; “High” : Mute
6 AGND – Audio Ground
7 O CH-RST – Reset output to changer
8 I Audio right channel
9 I CH-REQC – Request input from changer; “Low” : Request
10 I CH-DATAC – Data input from changer
11 O CH-DATAH – Data output to changer
12 I Audio left channel
13 I/O CH_CLK – Clock input/output for changer

Kenwood Connector Picture

The following works only with newer kenwood radios.

Older models have the same pinout but use some more simple protocol …

The clock low and high periods had a length of 4us.

The data is transfered in bytes ( 8 bits … MSB first ), data is valid at
the rising clock edge..

The data transfer is initiated either by the radio or the changer, the initiator
just pulls its fs line low.

When the changer starts the communication it gets 40 clocks from the radio
( 4 bytes addr + 1byte data size ).

The radio then sets its fs to low if it accepts the transfer.

When a transfer is initiated by the radio by setting its fs low it waits for
the changer to answer with a low fs,

then it sends the 4 byte addr header, the size byte for the data and the data.

Packet header, direction: both
byte log value ( r->cdc) description
0 0x29 destination address
1 0x10 destination address
2 0x1E own address
3 0x00 own address
4 x data size in bytes
5 x first data byte
4+data size x last data byte

From this point I only write the data part of a packet

initialisation handshake answer, direction: cdc->r
byte log value description
0 0x11 command identifier
1 0xA4 cycle numer of the above packet
2 0x00 ??
3 0x01 ??
4 0x02 ??
send after above packet, maybe radio identification and
caps, direction: r->cdc
byte log value description
0 0x20 command identifier
1 0x00
2 0x11
3 0x01
4 0x03
5 0x0B
6 0x0B
7 0x07
8 0x05
9 0x83
10 0x84
11 0xC0
12 0xC1
13 0xC2
14 0xC3
15 0xC4
16 0xC5
17 0xC6
send after above packet, maybe init ack from radio, direction:
byte log value description
0 0x20 command identifier
1 0x01
2 0x11
3 0x29 changer address
4 0x10 changer address
5 0x00 maybe last bytes of cmd 0x11(cdc->r)
6 0x01 maybe last bytes of cmd 0x11(cdc->r)
7 0x02 maybe last bytes of cmd 0x11(cdc->r)
changer caps info, send after above packet, direction: cdc->r
byte log value description
0 0x70 command identifier
1 0x02
2 0x0A maybe disc count
3 0x3F
4 0x03
5 0x0C
6 0x02
play position info, direction: cdc->r
byte log value description
0 0x60 command identifier
1 0x02 maybe sub command id
2 0x00
3 0x00
4 0x00 error code, 0 is no error
5 0x00 changer status ( load, eject, ….. )
6 0x02 play status (1 – play, 2 – pause )
7 0x00
8 0x01
9 0x00 track order mode ( normal 0, tscan 1, dscan 2,random 6,
10 0x04
11 0xBB some bcd number field, displayed when field 3 != 0
12 0x01
13 0x0B track number
14 0x07 disc number
15 0x01 min ( bcd )
16 0x22 sec ( bcd )
17 0x62 min disc ( bcd )
18 0x26 sec disc ( bcd )
19 0x09 min remain ( bcd )
20 0x30 sec remain ( bcd )
text info request, direction: r->cdc
byte log value description
0 0x42 command identifier
1 0x02
2 0x07 disc number
3 0x0A track number
4 0x00 text section number, sections had 12 bytes size here
5 0x00
6 0x80 text id ( 0x80 -> name 0x81 -> artist )
text info send after request, direction: cdc->r
byte log value description
0 0x62 command identifier
1 0x02
2 0x07 disc number
3 0x02
4 0x0A track number ( 0 -> disc title transfer )
5 0x00 text section number, sections had 12 bytes size here
6 0x09
7 0x00
8 0x80 text id ( 0x80 -> name 0x81 -> artist )
9..20 x text
commands send when keys on the radio were pressed, direction:
byte log value (play) fwd(toggle) bwd(toggle) disc-(toggle) disc+(toggle) description
0 0x50 0x50,0x50 0x50,0x50 0x50,0x50 0x50,0x50 command identifier
1 0x02 0x01,0x04 0x01,0x04 0x02,0x00 0x02,0x00 maybe event id ( 0 all up, 01 down, 02 toggle, 04 up, 06
hold )
2 0x02 0x02,0x02 0x02,0x02 0x02,0x02 0x02,0x02
3 0x00 0x02,0x02 0x02,0x02 0x00,0x00 0x00,0x00
4 0x07 0x01,0x01 0x02,0x02 0x04,0x00 0x02,0x00 key id
5 0x00 0x05,0x05 0x06,0x06 0x00,0x00 0x00,0x00

Using the information above you should have some starting point if you are
intrested in doing your own project, it is simple to build

a converter to send and receive these commands using a pc so you can find
out the meaning of other commands and fields if you need.


The pioneer IP bus uses a 2 wire differential signal for communication.

An equal level on both lines is a logical low while a high is encoded as a
voltage difference of some 100mV.

The data transfer is initiated by either the cd changer or the radio.The initiator
generates a high pulse ( ca. 170us ) and a following low pulse ( ca 20us ).

Then the data transfer starts, a 1 is encoded as a high-low sequence with
a duration of ap. 20us for both levels and a 0 consists of a 33us high and
a 7us low pulse.

The data is now transfered in bytes with MSB first, the 8th bit is an odd
parity bit.At the end of the 3rd and all following Bytes there is an additional
bit inserted after the parity where the receiver acknowledges the transfer.

This is done by holding the data lines in a high state after the initiator
sets them low.If this ack is missing the transfer is stopped.

The timings may vary because the real data is encoded in the pulse to space
length relation.

The first 3Bytes seem to be some kind of device address.The changer I used
transfered a 0x88,0x68,0x00 here while the radio sended 0x88,0x08,0x06.

The next 4 bits were always high. After that a size byte and then size bytes
were transfered. The last byte in the transfer is a checksum generated adding
the values of all data beginning with the 4bit sequence ( = 0x0F ).

In the following part I only will write the raw data excluding size and cheksum

Each command transfered was first answered by some acknowledge packet consisting
of a single 0xA1.

(which looks like: 0x88 0x08 0x06 0xF 0x02 0xA1 0xB2 -> 0xB0 is the checksum

The following packet sended by the changer contained the time disc and track

Byte 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Info command modus mcd disc min sec track cdt
Data 0x61 0x10 0x06 0x01 0x20 0x04 0x16 0x01 0x06 0x01 0x00 0x00 0x01 0x00 0x3F 0x00 0x00 0x00 0xC0 0x48


Value 0x02 0x07 0x08 0x10 0x11 0x13 0x14 0x15 0x16
Info ready track blink pause ready and disc blink disc blink load and disc blink eject and disc blink load eject

cdt: bit0: (1:cdtext),(0:normal)

The text information was encoded within this packet

Byte 0 1 2 3 4 5 6 7 8 9 10 11 12 13-22
Info command modus disc track text seqence number text
Data 0x61 0x10 0x06 0x01 0x20 0x04 0x38 0x09 0x00 0x06 0x00 0x00 0x00 0x00

Recommend link: Vitaliy’s Page @
with IP bus interface on AVR basis and more IP bus informations

Pioneer Transfer Logs
Pioneer Transfer Logs
4.3 KB

Possibly pinout of Pioneer headunit in Renault Espace III


The protocol panasonic uses is of the serial sync. type. There is one data
line, a clock line and a sync line the changer uses to send data to the radio.

The radio to changer communication is done by some signals known from standard
IR remote controls (without a carrier) using one dataline.

This remote control signal is pulse width modulated,the dataline is active

After an initail high(9ms) low(4.5ms) there follows a 32 bit sequence with
a 0 encoded as 550us high,550us low and a 1 as 550us high,1.7ms low.

If the low pulse in the init phase is only 2.25ms long it is just a signal
send periodical when a key is hold down and there are no data bits.

The data is transfered lsb first, the 1st byte is 0xFF-0th byte and the 3rd
byte is 0xFE-2nd byte.The 2nd byte is the command.

The changer to radio communication transfers the data in bytes msb first,
the data is valid at the falling clock edge and a low pulse of one half clock
period is sent after the first and the last byte of the transfer on the sync
line..The clock period is arround 8us.

There was only one packet containing state, time, disc and track information.

Byte 0 1 2 3 4 5 6 7
Info disc(b0-b3) track min sec state
Data 0xCB 0x42 0x09 0x02 0x56 0x00 0x30 0xC3


Value 0x00 0x10 0x20 0x04 0x08
Info normal scan random random repeat

Recommended links:

Panasonic CD Changer
Emulator – PIC 16F84A controlled

by Matthias Klumpp
– Descripting an Atmel based Panasonic CDC simulator
for VW and Audi car radios.
(Languages: German, English and Portuguese)

Alpine M-Bus

For informations about the Alpine M-Bus protocol see this page:

Joerg Hohensohn Webpage - Offline Copy
Joerg Hohensohn Webpage - Offline Copy
160.8 KB

Volkswagen VW


Pre-assembled boards that let people use the VW CD Changer connector
for auxilary audio inputs.

Schematic diagrams and firmware source code under GNU GPL available.

Ed Schlunder’s VWCDPIC
– VW CD changer emulator / audio interface


This should be the pinout for the Clarion 13-pin DIN connector which is used
for Clarion C-Bus.

Ford ACP

The following informations are taken from Andy Hammonds Yampp3/USB MP3 player
firmware with ACP protocol support.

Yampp3/USB Firmware with ACP Support
152.8 KB

Ford ACP is a network protocol used by the Head Unit to communicate with
and control audio devices such as the Ford 6 disc CD Changer and the Nokia
integrated cell phone or Ford Telematics units.

It is based on RS485 with 9 bit character data at 9600 baud.

A MAX-481 low power RS485 transceiver will work as interface between a serial
USART and ACP bus.

Pin Function

1 ACP +

2 ACP Shield


4 n/c

5 Audio Left +

6 Audio Right +

7 ACP –


9 +12V Power (unfused)

10 Audio Shield

11 Audio Left –

12 Audio Right +

You will need an AMP plug to connect to the head unit.

AMP Multilock Series 40 cable connector housing with 12 pins or sockets.

The CDENABLE line is 0V when the radio is off and +10V when it is on and
can be used as a standby switch for the yampp.

It is not a power supply and can’t drive a relay directly.


* a delay of 1642us (16 Bit times) will indicate a start of new message

* the 9th bit in a byte must be set in the last byte of message to indicate
the end of message

* Acknowledge is given with 0x06

Byte 0 – Medium/Priority, should be 0x71

Byte 1 – Changer functional address, should be 0x9A or 0x9B

Byte 2 – Head unit address, 0x80 on receive, 0x82 on transmit

Byte 3 – Command control byte

  • 0xE0 – Handshake 1, byte 4 should be 0x04
  • 0xFC – Handshake 2, byte 4 must be the same for transmit and receive
  • 0xC8 – Handshake 3, byte 4 must be the same for transmit and receive
  • 9xFF – Current disc status in byte 4
      • Byte 4 – 0x00 Disk OK
      • Byte 4 – 0x01 No disc in current slot
      • Byte 4 – 0x02 No disc at all
      • Byte 4 – 0x03 Check current disk
      • Byte 4 – 0x04 Check all disc
  • 0xC2 and 0xD0 – Change or request current disc
      • Byte 1 – 0x9A – command to change disc
      • Byte 1 – not 0x9A – request current disc
      • Byte 4 – disc number
  • 0xC1 – Control command
      • Byte 4
        • Bit 0 – Fast search
        • Bit 1
        • Bit 3
        • Bit 4 – change Random status
        • Bit 5 – change Loudness status
        • Bit 6 – change Play/Stop status
        • Bit 7
      • Send back byte 4 with actual mode
  • 0xC3 – Next track
      • Byte 4 – Track number
  • 0x43 – Previous track
      • Byte 4 – Track number

The last byte in all message is a checksum of all previous bytes. Simply add
all bytes of message to calculate the checksum.

Message examples

To display current play time, disc and track number:

Byte 0
Disc No
Track No

No disc message:

Byte 0

All informations are given without guarantee. Please mail for update or change

Ford Audio Control Protocol (ACP) Specification
2.3 MB
ACP Monitor
ACP Monitor
1.1 MB

Renault (Tuner
List / Update List)

This project aims at PC emulation of a VDO/Dayton CD changer (CDC) compatible,
among others, with the factory “Tuner List” head units of Renault
and Dacia cars since 2000. Higher-end “Update List” models, although
they provide an analog auxiliary input, can still enjoy some benefits using
this project, including improved sound quality thanks to SPDIF.

The emulator site:

The protocol description:

Toyota AVCLan

Interesting site about the Toyota AVCLan protocol for multimedia devices
including protocol details and emulator hardware to access the AUX-In input
on Toyota car audio units.

Chrysler / Jeep / Dodge

The given informations are only valid for Chrysler / Jeep OEM radio with J1850 VPW (PCI) bus connection between radio and CD changer. (most radios before 2005)

Example: Chrysler Radio 1 or Chrysler Radio 2

Communication between radio and CD changer works over the cars J1850 VPW bus system. This bus is in accordance with specification SAE J1850, the protocol uses one byte header frames in accordance with SAE J2178.

The radio will poll the changer with the following frame:

Frame header 0x8D CD Changer control frame
Data byte 1 0x0F Poll to CD changer
Date byte 2 0x00 Actual Radio mode0x01 = Radio off0x10 = Internal CD drive

0x20 = Mode MW or LW

0x21 = Mode FM

0x24 = Mode CD changer


The following frame is the poll response if changer is in idle mode or changing disc/track:

Frame header 0x8D CD Changer control frame
Data byte 1 0x93 Response to frame 8D 0F – Pong from CD changer when in idle status
Data byte 2 0x01 Actual disc, range 0-0xFF, Hex coded0-9 = numbers 0-9A = ‘:’

B = ‘;’

C = ‘<‘

D = ‘=’

E = ‘>’

F = ‘?’

Data byte 3 0x01 Actual track, range 0-0xFF, Hex coded0-9 = numbers 0-9A = ‘:’

B = ‘;’

C = ‘<‘

D = ‘=’

E = ‘>’

F = ‘?’

Data byte 4 0x80 Display control0x02 = Blinking “SCAN” text0x04 = “RND” activated

0x30 = “NO MAG” text

0x60 = “NO DISC” text

0x70 = “–:–” steady

0x80 = Disc number + radio clock

0x90 = Disc number + track number + radio clock

0xA0 = Disc number + track number + “00:00”

0xB0 = Disc number + track number + song play time


The following frame is the poll response if changer is playing a track:

Frame header 0x8D CD Changer control frame
Data byte 1 0x94 Response to frame 8D 0F – Pong from CD changer while playing
Data byte 2 0x00 Actual minutes of play time, range 0-99, BDC codedIf byte is 0x9x the time is displayed like “-0:00”, remaing time
Data byte 2 0x00 Actual seconds of play time, range 0-99, BCD coded

This frame must be send before the first 0x8D 0x94… frame, otherwise time update is not possible:

Frame header 0x8D CD Changer control frame
Data byte 1 0xE1 Command to activate time displayRequired before 8D 94Otherwise play time update not possible
Data byte 2 0x01 ???
Data byte 3 0x10 ???

The following frame will be send from radio to the changer, if a changer related button was pressed:

Frame header 0x3D CD Changer control frame, button press
Data byte 1 0x12 ???
Data byte 2 0x810x830x84 ??? With “TUNE” and “SEEK” button??? With “DISC” button??? With “RND” button
Data byte 3 0x26 Key ID0x23 = Button “TUNE FF” pressed0x24 = Button “TUNE RW” pressed

0x25 = Button “TUNE” released

0x26 = Button “SEEK UP” pressed

0x27 = Button “SEEK DOWN” pressed

0x35 = Button “RND” pressed

0xF1 = Button “DISC UP” pressed

0xF2 = Button “DISC DOWN” pressed


To activate the CD changer audio inputs you simply answer the poll frame 0x8D 0x0F with response frame 0x8D 0x93.

Be aware that the CD changer bus (J1850/PCI) is the same bus where all other control boxes are connected together, like ECU, RKE or SKIM module. So be carefull while handling the bus, mistakes can lead to serious damage on your car.

Radio connector pinout:

Chrysler Radio Connector
Valid for this type of connector.

Radio Connector
Pin Layout Code Description
1 BATT Fused B+ (IOD)
2 AC Fused Ignition Switch Output (run-acc)
3 P-LAMP Panel Lamp Driver
4 Side-M ???
5 NC No Connection
6 NC No Connection
7 RF- Right Front Speaker +
8 RF+ Right Front Speaker –
9 LF- Left Front Speaker +
10 LF+ Left Front Speaker –
11 GND Ground
12 BATT Fused B+ (IOD)
13 P-ANT Ant/Amp Remote (12V Output during Radio ON)
14 J1850 PCI Bus
15 EVA-MUTE Speaker Mute Input (Low active)
16 NC No Connection
17 NC No Connection
18 LR- Left Rear Speaker –
19 LR+ Left Rear Speaker +
20 RR- Right Rear Speaker –
21 RR+ Right Rear Speaker +
22 GND Ground
CD Changer Connector
Pin Layout Code Description
1 CDC R CD-Changer Audio Input Right
2 S-GND Shield Ground
3 GND Ground
4 J1850 PCI Bus
5 CDC ACC CD-Changer Ignition Switch Output (run-acc)
6 CDC L CD-Changer Audio Input Left
7 GND Ground
8 NC No Connection
9 RDW ???
10 CDC BATT CD-Changer B+ Output

Chrysler/Jeep CD changer emulator

Hardware schematic and layout:

J1850 VPW CDC Emulator Hardware
J1850 VPW CDC Emulator Hardware
Version: 1.0
186.7 KB

Firmware file:

J1850 VPW CDC Emulator Firmware
J1850 VPW CDC Emulator Firmware
Version: 1.0
28.8 KB

67 thoughts on “CDC Protocols

  1. Hi! Is anybody know, what should i write in the high / low configuration bits in the programmer, when i would like to build the Chrysler / Jeep / Dodge J1850 VPW CDC Emulator? I did not find related infos in the firmware zip…

  2. I am really struggling to find a protocol definition document outthere for a communications protocol between old pioneer HU units (with radio, tape and CD changer function) and 2 or 3 different cd changers models(cars are for years 1992 to 1996). The hardware is used in different Lexus and Toyota cars.

    In essence, the hardware uses two channels, one is a master (txm+, txm-) and the other is the slave (txs+ and txs-), I think the master is the HU and the slave is the changer. The HU will not activate the CD changer function if the changer device is not connected to this bus, I want to know if this scheme follows any kind of existing document outthere, so far I am finding nothing.

    Thanks a lot.

  3. I tryed dowloading the FORD ACP files for spec and monitor from above, but appear to get bad files. cannot unzip or look inside.

    I am trying to “braek” into my 98 FORD Explorer Premium sound to provide MP3/XM audio input. i now know that tapping into the CD signal is not enough as the HU is expecting a command from the Protocol wires about cd presence and what is palying. i feel i should be able to create a serial communicator to trick the HU to thinking cd is playing while not actually having the CD changer installed.

    any ideas?

    • Download again and use 7zip to open the files.

      Ideas? No, never worked on ford protocol.

  4. I Love this information. I wish I had a little bit more knowledge in my head as Im trying to fool my old Nakamichi CD-350 into using the changer input as an AUX Input, and also maybe use the head unit to do simple track forward, and back.

    Anyone up for the task of helping me out? 🙂


  5. Hello, Michael. I’d like to thank you for this article.
    Also I’d like to ask you about hardware shematic of Chrysler/Dodge/Jeep cd changer emalator.
    J1850_cdc_emulator rev.B.
    The PDF file with hardware shematics & layout contains the following annotation:
    R8/D4 designed for at least 315 Ohm bus load. Do not keep the J1850 line in HIGH state without load resistor.
    But I see no R8 and D4 in shematics.
    By the way: is R4 = 47 Ohm, not 47 KOhm?

    Thanks a lot!

    • BAT is the direct connection to battery and always under power.
      ACC is switched power supply, usually when ignition is switched ON.
      Can be tied together if needed.

  6. Many thanks for your answer.
    Now, that means that this short don’t let think the radio that there’s a cdc connected…

  7. Michael, is it possible to use bc548b instead of bc548a in Chrysler/Dodge/Jeep cd-changer emulator?

      • I’d like to refine the Chrysler cd-changer connector pin-out.
        9th pin is PDW that means Panel lamps dimmer signal.
        3rd pin is Shield.
        2nd pin is Audio ground.
        7th pin is Power ground.
        Also, Michael, I’d like to ask you if it is better to add a key transistor in Chrysler cd-chagner emulatror shematics? It will give the possibility to connect the power not constantly, but only when there is volltage on ACC.

  8. Maybe stretching the topic a little but I was wondering if there was any info available on the Kenwood head unit’s wired “Remote Control” interface? I’m trying to build my own custom steering wheel interface using an AVR microcontroller. I have the front-end completed & working perfectly on an ATMEGA328 but can’t figure out the protocol and/or cmds to send to the Kenwood? FWIW my hu is a DNX9960 & any info would be

  9. Hi, does anyone know where I can purchase an interface adaptor to connect a Sony 6 disc changer (T69) to my OEM Chrysler PT Cruiser (2004) head unit, please?

  10. hi I’m interested in putting together the circuit Emulator J1850 VPW unemployment CDC I have doubts that serves k4 (ISP) and that by the firmware program ATTINY20-16PC

  11. Hello,

    I stumbled upon your project while searching the web. I want to activate my CD changer audio ports on my stock radio (it’s a 2004 Chrysler unit), so I can plug in my mp3 player. I don’t have a CD changer. I don’t really need full control, I just want to be able to play audio through the ports. What is the easiest way i can do this?

    Under the chrysler page I read “To activate the CD changer audio inputs you simply answer the poll frame 0x8D 0x0F with response frame 0x8D 0×93.” How do I achieve this? Do I have to build the hardware completely?

    My digital electronics knowledge isn’t so great; i don’t understand what it means to “poll headers” etc..and my hex code knowledge is small. So if it’s not hard and you could explain it to me in simple terms. i I would be very thankful. Thanks.

    • Below the Chrysler/Jeep chapter you will find the hardware and software that fit your needs. (J1850 VPW CDC Emulator)

    • 1. The last letter of BC548 tels only the voltage amplifying factor. Any will do, A, B or C.
      2. ATtiny26-16PU is just fine

      Are these the only two connectors of your radio?

      • What are you mean: “Are these the only two connectors of your radio?”
        I have this stereo:
        stere front

        Stere back

        I use cd-box connector (gray cable) – back side of stereo

        And second is audio cable (black) with 3,5mm jack to my phone.

        I think that I must control cd-box cable pinouts…

        I use cd-box connector (gray cable) – back side of stereo

        And second is audio cable (black) with 3,5mm jack to my phone.

        I think that I must control cd-box cable pinouts…

        • The radio is different than mine and never saw this before, seems to be an older model. A wild guess but I think the CDC control is different to my implementation.

        • Hi hmm, 5 years later I did make this emulator too. I have older 2001 chrysler radio with DIN-8 CDC port. Emulator is not workig. Did you manage to make it work ?

          • I did manage to make it work with 2001 radio after all.
            two things were needed:
            1/ a delay between ping and pong (I used 5ms)
            2/ special message on startup as follows
            0x8D 0x91 0x04 0x02 0x01 CRC
            0x8D 0x92 0xC0 0x00 0x00 CRC
            0x8D 0x93 0x00 0x00 0x00 CRC
            0x8D 9×96 0x00 0x00 CRC
            maybe not all of the four messages are needed.
            I did also add code to work with buttons. Then you can control ipod through radio buttons.
            messages are :
            Disc UP…..0x3D 0x12 0x81 0xF1 CRC
            Disc Down 0x3D 0x12 0x81 0xF2 CRC
            FF…………..0x3D 0x12 0x83 0x25 CRC
            RW…………0x3D 0x12 0x83 0x29 CRC
            Seek+…….0x3D 0x12 0x83 0x26 CRC
            Seek-…….0x3D 0x12 0x83 0x27 CRC
            Random on 0x3D 0x12 0x84 0x35 CRC
            Random off 0x3D 0x12 0x84 0x30 CRC

  12. Michael, please, help me. I’d like to connect some device to AUX of cd changer’s connector of my cd player (alfa 147 – original Blaupunkt)

    | Blaupunkt ( DMS ?? )
    | It is basically a 2 wire (rx/tx) async. serial protocol with 9 bits of data where the 8th bit is used for synchronisation.
    | That made it easy to interface it to a player or PC because you can use the serial port.

    Pin 13 asci bus CDC>RO
    Pin 14 asci bus RO<CDC
    Pin 15+12 permanent
    Pin 16+12Vswitched
    Pin 17digital earth
    Pin 18audio earth
    Pin 19 CDC left audio
    Pin 20 CDC right audio

    Like I understand, 18/19/20 pins – AUX; I must connect rx/tx to 13/14 pin and receive/send signals via some program (like hyperterminal) to emulate cd changer . Also I can do special scheme, based on Attiny xxx (also i must to program it), isn't it?

    What program I must to use to connect via rx/tx? What signals i must to send? rx/tx is on ttl level (3.3v or 5v or higher)?
    If it possible, can You say, what scheme I must do, what hex I must to program in Attiny xxx (xxx -?)?
    Sorry for my English.
    Thank You.

    • Can’t help you here. I never worked with Blaupunkt. The information I have are just a backup of a webpage which no longer exists.

  13. hi

    i am trying to detail the ip-bus (pioneer) communication protocol – and am trying to create a small circuit to capture the communication between the changer and hu. I see that you have already created a similar circuit – using a AT90S2313 controller

    It will be great it you can also share the details of your circuit (schematics + code)

    Thanks in advance

    I will share back the protocol details if and when I succeed


  14. Hi,

    I am trying to enable my aux button on my Ford Focus 2007 radio, it is a can bus unit and the only info that I am getting from the HU is
    id:3E8 DLC:8 2,0,10,14,0,0,0,0
    id:50c dlc:3 c,4,0
    any idea where I can get more info on the hand shake with this unit.



  15. Your picture of the HU in the Espace is right in that it’s a Pioneer unit but it doesn’t use the protocol described. Instead it’s a single ended synchronous bus called either P-BUS or M-BUS. I have decoded the protocol sufficiently to create an MP3 player using the VS1011 and an SD card which is controlled by the steering column controls or the remote control. It was initially based upon the idea here: although the code doesn’t bear much resemblance any more. If you are interested I can send the details of the bus and protocol.

    • Hi Rob, I drive an Espace with the Pioneer system installed and would like to add a MP3-player. I’m interested in your details about the bus and the implementation of the player. I would be glad to get some information from you.

      • Shows how often I read this. If you’re still interested let me know and address and I’ll send the info.

        • Hi Rob, I’m still interested in the information. Please contact me under lake.constance(at)
          Thanks H.-J. from Germany

        • Hi Rob and H.-J,

          Would it be possible to also send me the infor?
          You can send it to bj(at)

          Best regards,

        • HI Rob,

          I’m interesting by your decoding of PIoneer P-BUS protocol. I’m owner of Renault Espace III and i’m searching everything for Pioneer SCU-2XXX and this display !
          Many thanks for reply if you read this (3 years ago !!)

        • Hello Rob

          I’m interested in your MP3 project with M-BUS comunication. Could you contact me? amr101dm (at) Thanks!

          Best regards,

  16. Hello, I just had a quick question, I downloaded the files for the Ford ACP protocol and im trying to take a look at the files in the yampp3 folder. What program was used to create the program?

  17. Hi, good day

    First I apologize for my unknowledge of electronic concepts.

    I’m very interested and I read your project for Chrysler/Jeep cdc emulator and I don’t understand, what ISP does mean? (K4 component), I guess it’s a kind of eprom memory or something like that but I’m not sure, and what is component model? or how can I ask for it at the store?.

    Finally, I’m guessing too, the firmware file is to program the ISP component? and how do I can do this? Someone at the store could help me for that?.

    Thank for your attention. Best Regards

    • ISP means In-Circuit-Programmer. It’s an interface to program the AVR from your PC. Any AVR programmer with STK500 compatible pinout will work. The following hardware will work out of the box: STK500, AVR-ISP or AVR-ISP MkII (all Atmel products).

  18. Has anyone built the Jeep CD Changer Emulator?

    Would you be willing to build one for me?
    Send me a price quote for it at my website. (don’t think I can post email here?)


  19. Hi, what is the emulator supposed to do? Can I connect an mp3 player trough it to be controlled with the Infinity unit?

    If thats the case, I can figure out where the input is in the schematic.

    Thank you!

  20. Hello, Michael! I have a strange issue with CDC emulator for Chrysler Sebring ’04. My radio is RBK without a tape player. I disconnected it from a car, took it home and used an old soviet power supply unit to power it with 12V. I connected 12V to pins 1, 2 and ground to pins 11, 22 of 22 pin socket, and plugged CDC emulator too. At home, using this system, it works just fine, it shows “disc 1, track 1, 0:00” as it’s supposed to and plays audio from 3.5mm jack. But when I took it back to my car and connected it nothing happened. It plays CD, works in FM/AM mode but doesn’t do anything when I press MODE button. I double checked it, it works at home perfectly. Can you possibly help me with my problem? Maybe there’s something I missed?

    BTW, binary file is broken so I had to recompile HEX-file in order to make it work.

    • There is usually a connection between the radio and the cars data bus.
      could be a problem that the emulator interferes with the car bus. You
      may try to connect just power inside the car and see if the radio
      works with the emulator. If yes then just connect the other wires one
      by one and see if it stops working at a certain wire.

    • Hi there!
      I have bought all electronic components from ebay. I believe all parts will came soon.
      WRT Sergei comment about broken binary file. can anyone share correct hex file?
      Really appreciate your support!

  21. Hi Michael,
    I also have the chrysler RBK stereo. Mine also does not detect when I change ^Disc to the emulator. Is there a switch of some kind to let the head unit know there is an acc attached? Is it looking for some resistance?

  22. Hello great program,
    I would build the project, how do get a 3k hex file into the ATtiny26 2k flash.

    • Using an AVR programmer that supports the ATtiny26. Please Google that, it’s covert a million times.

  23. Hi colleagues.

    How does the CD Changer protocol used by Skoda Symphony CD player looks like electrically?
    I did not find something relevant.

    I would need this info in order to build my own project for AUX-in for this radio-CD.

    Thanks in advance.

  24. Hello, i am trying to turn on a factory radio for a hummer h3 2008 on a bench outside of the car, and would like a little help. It is a class 2 vpw j1850 radio, and i have the serial data pin of the radio hooked to pin 2 of an elm327 bluetooth. I would like to know what mode and pid should i call to simulate the BCM or other module of the car when it is telling the radio to turn on. Pac manufactories GM turn on interfaces but they are for gmlan 11 bits and 24 bits. Class 2 is a little bit older. Anyone have a clue?

  25. Hello, my name is Anatoly and I want to ask you about cd changer Kenwood KDC-C660 is compatible with Audi Concert 1 and if it is compatible how to connect them.

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