ALDL info

DAN FURGASON furgason at hg.uleth.ca
Thu Apr 17 18:07:01 GMT 1997


For all of you trying to decipher the ALDL bit stream here are a few "bits" of
information:

Each bit begins with a Hi to Lo transition at To. If the bit is a 0 the line
goes Hi at T1. If the bit is a  1 the line remains Lo until T3 and then goes
Hi. The data is sampled at T2. The next bit begins at T4. 


***   +++++++++++******      + = "0" timing
  *   +         .     *      . = "1" timing
  *   +         .     *      * = Common timing
  *   +         .     *
  *   +         .     *
  ****+..........     *   
  To  T1   T2   T3    T4

To --- Start of bit
T1 --- "0" Transition
T2 --- Receiver Sample Time
T3 --- "1" Transition
T4 --- Start of next bit

To - T4   6.25 msec
To - T1   .2 msec
To - T2   1.5 msec - 2.3 msec (data valid Period)
T3 - T4   .5 msec minimum

Here is the ALDL Transmit Table for an 89 Suburban

PROMIDA
PROMIDB
ISSPMP
ADCDOL
FILTMPH
ADMAP
NTRPMX
ADTHROT
INT
ADO2A
MALFFLG1
MALFFLG2
MALFFLG3
MWAFL
MWBG
ADBAT
OLDPA3
BLM
ALDLCNTR

The stream is begins with a sync character (9 "1's") then the transmit table.
Each successive byte in the stream is preceded with a "0" start bit.

Dan Furgason



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