ABS ALDL comms

[ae2598 at wayne.edu]

How many systems, other than the ECM, communicate on the ALDL?   Do ABS
controllers have any comms capability?

On Fri, 17 Nov 2000, Dale Klein wrote:

> 
> 	Probably a few people have done this before, but gee it was fun.  Running 
> in & out of the house with cables & computers & gizmos.
> 	I got to borrow a tech 2 today.
> 	On my '95 Z28 LT1, I plugged that into the aldl port, and had the laptop 
> also listening on the aldl.  I had the tech2 ask the abs module for data, 
> and recorded the comms on hyperterminal on the laptop.
> 
> Does anyone out there have any info about abs module aldl 
> communication?  Even if it's just small caliber stuff like below that'd be 
> neat.  I'm thinking, (and have heard others thinking) that it would be neat 
> to have your logging program (pcmcomm, freescan, carbytes, tts, palm 
> pilot!!!, or whatever) ask the abs module for front wheel speed.
> Any comments or advice? (see the myriad questions below)
> 
> Thanks, Dale
> 
> 	So a description of what seems to happen:  (let me know if you'd like a 
> copy of the 9k file, I'll put it on incoming if anybody wants).
> 
> 	first there's chatter, I think just from the pcm, but maybe not, before 
> the tech2 was set to display abs data
> 
> then tech2 - abs module messages, vehicle not moving.  request alternates 
> with reply
> 
> request, looks like it at least, always the same
> F1 AF 01 5F
> 	header is F1 AF, 01 is mode or message
> 	5F is normal checksum. add first bytes, not, add 1 = checksum
> 
> while not moving, brake off I think
> F1 E6 01 20 E9 9E 91 F0
> 	shorter messages, E6 can't be message length.
> 	note 20 E9 9E 91 are similar to last 4 data bytes of other messages...
> 	F0	correct checksum
> 
> in between not moving & moving, message gets longer..?
> F1 E6 01 01 01 20 E9 9E 91 EE
> 
> while driving, low speed, very light accell, reply looks like, message even 
> longer...?
> F1 E6 01 0F 0F 0F 0F 0F 20 E9 9E 90 AE
> 	header is F1 E6, 01 is mode or message,
>     but second byte E6 is not the same kind of message length (AF + 9 != E6)
>     maybe there is a different definition of message length?
> 	0F 0F 0F 0F 0F looks like 4 wheel speeds & vehicle speed, could be bit=mph?
> 	20 E9 9E 8F	unknown. one bit somewhere in there may be brake light on/off
> 	AE 	checksum, but 2's complement checksum would be A6..., right? are there 
> other sorts of checksums?  double checked a couple messages from this spot 
> in the stream, and they both come out wrong?  doa!
> 	
> while slowing back down, low speed, light decel, brake on
> F1 E6 01 07 07 07 07 07 21 E9 99 91 D1
> 	D1   checksum, but 2's complement checksum would be D1... how bout that.
> 
> and coming back to a stop
> F1 E6 01 01 01 21 E9 9E 91 E9
> F1 E6 01 21 E9 9E 91 EF
> 
> later the tech 2 asks for the module calibration number data, etcetera,
> 
> and then chatter again, when tech2 not asking for abs data.
> 
> 
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