[Information] ALDL Basics

160 And 8192 Baud Aldl
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[Information] ALDL Basics

Postby VL400 » Sun Aug 09, 2009 1:23 pm

About: This information will be updated from time to time and serves as a basic introduction to GM ALDL, specifically aimed at GM Holden Commodores.


What It is and What Can It Do: ALDL stands for Assembly Line Diagnostic Link. It is used for a variety of things from, as the name suggests, initial system testing when the vehicle is manufactured to vehicle module communications to diagnostics at the dealer/home to real-time tuning. There are a few different implementations of ALDL…

VN/VP – This was the first implementation, was also the most basic and is the only implementation that uses ALDL for purely diagnostic purposes. It operates at 160 baud and is a uni-directional (read only) data link. The ECM uses a ‘bit-banging’ technique on the CEL (Check Engine Light) wire to flash data out bit by bit. Bit banging is a method to transmit serial data using only software rather than a hardware UART. It is ok for slow data speeds but puts too much load on the microprocessor for high baud rates. The 160 baud rate is due to the ECM operating with 6.25ms minor loop interrupts. On every interrupt a bit is applied to the CEL wire, 6.25ms = 160Hz or 160baud. When ALDL is enabled the CEL will flash with the data.

VR/VS – The second and probably the most widely used type is 8192 baud, this is also used in many GM built US vehicles from the mid/late 80s to the late 90s and often referred to as OBD-I. It is a bi-directional half-duplex data link using a hardware UART in the processor and a Delco/Delphi transceiver IC. The purpose of the transceiver is to convert the transmit and receive lines of the processor UART into a single wire half-duplex data bus to allow the ECM to communicate on the vehicle bus. It is no longer related to the CEL wire. This data bus allows for only one device to communicate at a time and connects all the major modules – BCM, ABS, SRS, ECM etc. In VR and VS applications the bus master is the ECM/PCM. Every device on the bus has a device ID, so when data packets are put on the bus it is ‘addressed’ to a particular device. This way only the device that is addressed process’s and responds to the packet, all the others ignore the data.
PCM Device ID - $F4 for VR V8, VR V6 and VS V8. $F5 for VS V6
BCM - $BD in VR and $F1 in VS
ABS - $F9
SRS - $F2


VT – This is a very similar implementation to the VR and VS ALDL. It is also 8192 baud but the major difference is the bus master is no longer the PCM but instead the BCM. The VT took the data bus further by also including the instrument cluster. A regular message containing all the dash information is sent at the request of the BCM.
PCM Device ID - $F5
BCM - $F1
SRS - $FA


VX and VY – The NA V6 uses a flash based PCM, this also added some new ALDL modes for the security system. The PCM is linked to the BCM, ALDL is used for the linking process.
PCM Device ID - $F7 for flash based PCM
BCM - $F1

How It Works: Due to the different types of ALDL there are different ways to get data out of the ECM…

VN/VP – This is a uni-directional data link so to enable ALDL data a resistor must be placed from the diagnostic enable wire to ground. This tells the ECM to start outputting data on the CEL wire. The disadvantage is on a factory memcal it also locks the spark advance to 10deg BTDC until 2000RPM, this can be disabled by editing the memcal binary. The data that is sent over 160baud ALDL is very basic and is a fixed data stream. It contains information on diagnosing faults and checking sensor outputs.

VR/VS/VT – Being a bi-directional data link it is now possible and necessary to request data from the ECM/PCM. No resistor is required to tell the ECM to start transmitting data. The ECM does not lock the timing to 10deg BTDC when requesting data so it is possible to drive the vehicle like normal while logging. The 8192baud ALDL is far more useful than the 160baud data for many more reasons than just being faster. There are a number of different ALDL modes…

Mode 0 – Clear All ALDL Modes
Mode 1 – Data Frames (There are many different message frames)
Mode 2 – Request 64 Bytes of Memory
Mode 3 – Request 6 Particular Bytes of Memory
Mode 4 – Control Mode
Mode 5 – Enter Download Mode (GM Development)
Mode 6 – Address Of Routine to Execute (GM Development)
Mode 7 – Broadcast Mode (GM Development)
Mode 8 – Disable Bus Chatter
Mode 9 – Enable Bus Chatter
Mode 10 – Clear Malfunction Error Codes
Mode 11 - New delcohacking.net mode or in VU/VX/VY part of the security system
Mode 12 - New delcohacking.net mode
Mode 13 - Security Seed/Key on Flash PCMs
Mode 14 - New delcohacking.net mode
Mode 15 - New delcohacking.net mode
Mode 16 - Flash PCM Write

The most commonly used modes are Mode 1, 2, 4, 8, 9 and 10

Mode 1 is used for getting the operating parameters out of the ECM, in mode 1 there are also many different messages. Each message is a fixed length and contains different parameters such as RPM, coolant temp, vehicle speed, etc etc. Each message contains different items for different logging/diagnostic tasks. Some messages contain engine params, some transmission (auto only) and others for when GM connect tech-1 to calibrate the unit.

Mode 2 is used to upload the binary (the contents of the memcal EPROM) from the ECM to a PC.

Mode 4 is useful to fault find sensors. It allows you to substitute or slew sensor values. For instance, it is possible to override the coolant sensor and substitute it with a different value to see what effect it has. Or you can slew (or offset) the temperature by a few degrees.

Mode 8 and 9 allows you to temporarily disable the ECM/PCM from attempting to communicate with devices on the bus. If you don’t issue a mode 9 (enable chatter) frame after a few seconds the ECM will resume its normal communications.

Mode 10 clears all the stored malfunction codes. If you are having problems and experience a CEL then a malfunction code will be stored in the ECMs RAM. It is possible to erase the codes by disconnecting the battery but this also clears other learning data so a mode 10 ALDL frame can be issued.

VU/VX/VY V6 Flash PCMs – These are locked from the factory. The locking is similar to how the LSx PCMs are locked using a seed/key combo. To unlock the PCM you must use mode 13 to request the seed. The PCM will send the unique seed value and then using mode 13 again you must send the key. If the key was valid you will be granted access to the PCM. You are still able to log data from a locked PCM but you cannot use mode 2 to get the calibration or binary.



Hardware: GM ALDL is a 5 volt, fixed pulse width, asynchronous data stream. The hardware to decode this so a PC can communicate with the ECM is very basic and usually only requires a few parts.

Interfaces can be purchased from this site….

USB Internal for VN/VP
USB ALDL Interface for VR to VY

Or if you prefer to make your own …
VN/VP – There are two parts required to get a PC working with a VN/VP ECM, one part converts the 5 volt signal to an inverted 12v so a RS232 serial port can read it and the other part puts the ECM into diagnostic mode.
An example can be found here.. http://winaldl.joby.se/aldlcable.htm

The data connector can be found near the ECM under the dash. It looks like this...
Image
Courtesy of TechEdge


VR To VY OBD-I – There are many different circuits for reading 8192baud ALDL. Some are simple and some more complex.

Basic circuit.. http://www.techedge.com.au/vehicle/aldl8192/8192hw.htm
Note: There is an error in this diagram, D3 needs to installed with the opposite polarity

More complex but also better.. http://www.geocities.com/MotorCity/Shop/1624/aldlif.jpg

The data connector can be found under the steering column and looks like this...
Image
Courtesy of TechEdge




Software: There are a number of different software packages available to scan, log and tune using ALDL.

A free and easy to use software package for 160Baud ALDL can be found at.. http://winaldl.joby.se/

Probably the most widely used software is TunerPro (http://www.tunerpro.net/) and ScannerPro (http://www.scannerpro.net/ however now that TP V5 has its own logging engine this is obsolete). Both are free to use and download, however for real-time tuning TunerPro asks for a small donation to remove a startup delay.

TunerPro and ScannerPro use files to define the ALDL stream, TunerPro V4 uses ADS files, TunerPro V5 and ScannerPro uses ADX files - however they are a different format. Some definition files can be found here.


ALDL In The DIY World: There are many limitations in the VN and VP application, the biggest two are slow and very limited data. This can be overcome by adding a small circuit to the ECM and using a VR $12 binary. Some information on a small circuit to enable 8192baud data can be found here http://delcohacking.net/forums/viewtopic.php?f=11&t=173 or if you would like to buy a kit or built board they can be found here http://delcohacking.net/forums/viewtopic.php?f=14&t=165 . You will also need to download and burn a $12 bin to the memcal. The OSE $12P bin will work well for this and can be found here or a standard bin can be downloaded from here.


TunerPro Getting Started Guide: While this guide is not specific to GMH it does cover the basics. Instead of using the XDF,BIN and ADX files they mention replace these with ones that suit your vehicle. Here are the links to download Holden specific definitions... ADX, XDF, BIN. A very handy alternative to downloading bins and XDFs is the memcal ID tool




Well that’s all for now, I will attempt to keep updating this post with new and additional information. Please let me know if you want any further info added or for any corrections.

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Re: [Information] ALDL Basics

Postby VNracer34G » Sun Aug 09, 2009 8:17 pm

VL400 you rock :punk: good to your word and fast too
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Re: [Information] ALDL Basics

Postby monaro308 » Mon Aug 10, 2009 8:57 pm

Thanks VL400....it answered a couple of questions i was going to ask...especially about the VR ECM not locking the timing to 10deg whilst tuning.
I knew the VN/VP did but wasn't sure with VR $12...cool.


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Re: [Information] ALDL Basics

Postby VNracer34G » Fri Dec 11, 2009 5:58 pm

Hi guys, i've been able to log successfully ( i think ) using WinALDL on 34G for a while now and been trying to interpret what i get with mixed results and varying degrees of confusion. Time, rpm, map, o2 (crossrefferencing with a af/r guage helped making sense of that ) BLM etc i think i have a reasonable grasp of. What i am having trouble with is where it tells me what the ignition timing is, the knock counts (shown on some comps supported but not the 808) and injector load (bpw?) now i'm sure theres going to be many of you going :wtf: at me but sorry i'm more at ease with my dial back timing light and trying to drag myself out of the dark ages :wall:

In advance of replies i'll say why the hell didn't i see that for myself you **** :rant: ************* :comp:
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Re: [Information] ALDL Basics

Postby delcowizzid » Fri Dec 11, 2009 7:42 pm

winaldl doesnt really show much on the 160 baud datastream no timing think there may be a flag for knock but i dont quite know but pretty much the nasics map mat coolant temp iac steps rpm etc
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Re: [Information] ALDL Basics

Postby VNracer34G » Fri Dec 11, 2009 8:02 pm

bollox, so what do you reccommend thats within 'budget' ?
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Re: [Information] ALDL Basics

Postby Holden202T » Fri Dec 11, 2009 8:05 pm

one of vl400's serial boards, allows you 8192 baud data stream and logging with programs that are a bit easier to read than winaldl.

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Re: [Information] ALDL Basics

Postby VNracer34G » Fri Dec 11, 2009 8:12 pm

one of them would be awesome man but out of budget - just going from weekly to fortnightly pay with a gap between and chrissy fast approaching, hell i had to arm twist to get a few bevvies in and get gas to go racing tomorrow night. Plus that'd get me trailered lol
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Re: [Information] ALDL Basics

Postby Holden202T » Fri Dec 11, 2009 8:24 pm

well i dunno :D

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Re: [Information] ALDL Basics

Postby VNracer34G » Fri Dec 11, 2009 8:32 pm

I've got tunerpro v4 downloaded but as far as i know i need to go RT to log with it don't i ?
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