Re: Mode $0a on 7730

["Paul Blackmore" <paul_blackmore@hotmail.com>]

> but now I realize that the author of that page intended the full string
> to be F4 57 01 00 XX, at least to enter Mode 1.  Why there's the extra
> 00 there, I don't know.  So the LEN byte should be $56 + message length,
> not including the mode ID?

The ALDL commands are split into four sections:
The ID byte
The Length byte
The data
The Checksum

The ID byte determines the module to which the command is sent.

The Length byte is the number of databytes +$55.
I've heard it said that the $55 is binary 01010101 which was chosen because 
it is the easiest value to "corrupt" with a noisy connection. Once it is 
corrupted the checksum would be wrong and the frame can be discarded.

The FIRST byte of the data determines the mode:
Currently I am only aware of the following modes - these may not be the same 
for all vehicles:

$00: Resume normal communications
$01: Request a TABLE of data
$02: Request a set of memory
$03: Request a block of memory
$04: Command the ECM
$05: unknown
$06: unknown
$08: Stop chatter
$09: Resume chatter
$0A: Clear malfunction codes

The second byte of data is special in the Mode $01 command - it determines 
the TABLE of data that is to be returned. A typical set of data tables would 
be:

$00 - Engine inputs/outputs
$01 - Engine inputs
$02 - Engine outputs
$03 - Tranmission inputs/outputs
$04 - Transmission inputs
$05 - Transmission outputs
$06 - Trouble codes
$07 - History codes

So the command $F4,$57,$01,$00,$XX would request data table $00
and the command $F4,$57,$01,$03,$XX would request data table $03
etc...


> What would a valid module response look like?

For the command $F4,$57,$01,$00,$XX
You should see a large block of data containing about 64 bytes (give or take 
a few) like this:

$F4,$98,$01,$00,$00,$00,$00,$AA,$7F,$35,$86,$00,$00,$00,$00,$21,$00,$64,$00,$60,$00,$07,$A6,$60,$80,$80,$80,$80,$00,$00,$09,$92,$5F,$FF,$90,$80,$22,$00,$00,$20,$7E,$00,$00,$00,$00,$5B,$00,$1A,$C7,$A5,$00,$00,$00,$00,$00,$00,$00,$00,$00,$09,$00,$00,$00,$00,$00,$43,$1C,$4F,$01,$C0

For the command $F4,$56,$0A,$XX
You should see something like your original command - not sure if it is 
exactly the same - I think it is.

Cheers
Paul

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