Chrysler CCD bus display

Page updated 07.10.2003




I have 1992 Chrysler Voyager. Since I have had the car I have been interested in its computer systems. Being late eighties technology the car is quite advanced. There are four computer systems talking to each other over Chrysler proprietary bus called CCD bus. Four systems are: Engine controller, transmission controller, body controller and instrument cluster.

I got real motivation for CCD bus hacking when transmission broke down little over 100k km. During the costly service I learned that A604 EATX controller provides some transmission quality data. Controller can measure every clutch condition. Conditions are displayed as CVI (clutch volume index) units.

I decided to build display unit with what I can follow transmissions condition. My early attempts to find any information about the CCD bus led nowhere. I forgot the project for few years. 2002 summer I started over and managed to find some information and build experimental CCD bus display.


The CCD bus

Physical layer is implemented with 2,5V centered differential signal. Bus is terminated with 120 ohm resistor. Bit framing is equal to normal asynchronous serial (RS232) framing. CCD bus protocol resembles CAN very much or vice versa. Transmission speed is 7812,5 baud. Odd speed comes from 1MHz / 128 = 7812,5.

Best public sources of CCD bus information are:

1. CCD bus patent papers. Found here: Search patent # 4,706,082

2. Obsolete Intersil (former Harris) CDP68HC68S1 datasheet or local copy if Intersil link does not work.

Protocol level is different story. No public information is available. You have to find out by the hard way how things work. Disassembling reverse engineering etc. There are few findings used and documented in my experimental software.


Pdf format schematics can be found here: Page 1 Page 2

There is no separate part list available. Part information is embedded in to the schematics. LCD display is not documented in the schematics. I have used 4 x 40 character Powertip PC4004 display.

Circuit is designed so that you can use almost any CCD chip what you can get hold of. Good source is old ecm, eatx, body computer etc boxes. All of then has one. Circuit is also designed so that you can implemented listen only CCD bus interface with comparator and software. I have not finished software to do this.

There are two extra uarts reserved for pc applications and future ideas.



Source code for PIC16F877 controller can be found here. Project is written with Hi-Tech PICC compiler.

There are few comments in source code. No other documentation is available.



In normal mode display unit is passive. It only listens bus traffic and collects some data packets. Collected data is decoded and displayed. If you short jumper J28 unit goes to diagnostic mode. It transmits some diagnostic function (test tool) codes to EATX controller. EATX sends back stored fault codes and clutch CVI indexes.

Unit power supply is done so that unit wakes up (power on) when CCD is active. In my car body controller computer wakes up and starts to transmit information when you open the door.



Circuit board what I made for this experiment

CCD display unit in use

Normal display

Fault code & CVI display


Other information