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ALDL Basics

  Last Updated 19 April 2001

The ALDL link is basically a single wire, bidirectional serial stream compatible with most UARTS. The serial data parameters are 8192 baud, 1 start bit, 8 data bits, no parity, and 1 stop bit. The baud rate is a slight problem, because standard DOS software doesn't directly support this rate. Instead you have to program the PC's UART directly, instead of using BIOS calls. However, under all Windows operating systems (3.1, 95, 98, NT4 and probably 2000) there are API calls available to set the correct parameters, so this shouldn't be too much of a problem.

Hardware

Before you can read data from the ECU, you need to be able to interface the ALDL port to a standard PC COM port. YOU MUST NOT DIRECTLY CONNECT THE TWO, or damage to the car, the PC or both may result. The standard RS232 signaling levels are +/- 12V, whereas the ALDL link is +5V. So you MUST uses an interface box. I don't see any point in reproducing all the details on how to do this, because everything you need to know can be found at http://www.andywhittaker.com/ecu/aldl_hardware.htm I have built the two transistor circuit shown here, and it works fine on my car. However, I realise that many people will not be able to build such circuits themselves. All is not lost though, as an Autobahnstormers member is preparing to produce a ready built unit for the job. Hopefully, this will be fully isolated version so that if either the PC or the ECU malfunctions, it won't damage anything else. If you don't feel you are competent to build the circuit, EMAIL me and I'll see what we can do you for.

Software

Once you have the hardware sorted out you need some software. If you followed any of the links on Andy Whittakers page, then you will see that most cars using the GMP4 ECU produce a continuous stream of ALDL data. However, the LC doesn't, unfortunatley. Instead you have to 'ask' the ECU to send you the required data, by sending it a command string. I am not yet certain how many command strings there are, but I do know there are at least 3 different ones. But, because you have to 'ask' the ECU for data, this means that Andy Whittakers Freescan program won't work without extensive modificaions. Feel free to make the modifications if you want, but at the moment, my preferred option is another peice of software written by an Australian for his Holden Commadore.

Carbytes V2 is a piece of shareware software that was written by Paul Blackmore. It can be downloaded from his website at http://www.blacky.co.nz/efilive The EXE zip is 485K, and the DOC zip is 1.2MB. You only need the .EXE, but the DOC is extensive and gives good instructions on how to use it, so I would recommend you download that as well. This software allows you to decode the ALDL data stream into 'real parameters' so yo can watch things like speed, rpm, injector pulse duration, water temperatures, turbo pressures, etc, etc. You can also plot realtime graphs, which should make very interesting viewing once I get some good data from a dry track day. It is also possible to log the data to disk for later analysis. I have made several 30 minuite runs in my car, but I can't post the results for legal reasons (don't want to end up before the courts !)  All you need to run Carbytes V2 is a setup file containing information about what the bytes in the ALDL data stream are. I don't have a full description yet, but you are welcome to what I do have. It can be downloaded from HERE. Please noted that the scalings on some values appear to be incorrect, but I am working on that.

The only problem I have with Carbytes is that it requires a PC with quite a lot of memory, and a reasonably fast processor. This is not a criticism of Paul's software, and I accept that most recent notebooks are perfectly adaquate. However, my notebook is only a 33MHz 486, with 12Mb of memory, and therefore isn't really suitable for running Carbytes (or Windows 95 for that mater). So I have written a couple of simple Windows programs to overcome these problems. They allow me to create data logging files on my pre-historic notebook, and then use Carbytes to look at the data on a faster desktop PC. Since others may find these programs useful, here they are. I have included the source code, which can be compiled using Microsoft Visual C++ Version 1.52. No warantee, implied or expressed, etc, etc, blah, blah

ALDL_LOG - This program will run, logging data to disk, untill you hit any key. It should be able to generate between 3 and 6 samples a second on most PC's. This is the program I use to log the data during track sessions. The logged data is in ASCII format, and is suitable for viewing using Carbytes V2.

PROMDUMP - This program reads the contents of the EPROM in your ECU and stores it to a file on your hard disk. Feel free to compare your EPROM with mine. I expect it will be the same, but it is possible that Lotus changed the program during the production run, so it could be different. If you find yours is different, could you please send me a copy so that I can take a look.