ISO-9141

[Land Shark]

At 10:24 PM 1/29/98 -0600, you wrote:

>ISO 9141 is just 10.4 Kb rs232 so can probably
> connect straight to computer.

 THWACK THWACK

 (Jim thumps head into PC)

 Will everyone PLEASE go read the spec..

 ISO-9141 is not a fixed baud protocol..

 10.4kbps is the MAX speed of the protocol

 Actual speeds I've seen are:

 2400, 4800, 4804 (yes, 04!), and 9600 in addition to 10.4

 Here's how it works..

 ECU's can either have a K line or a K & L line

 Initializing comms with the ECU's is either done by grounding
 the K or L or both lines or by transmitting a one byte address
 at FIVE baud (yes, 5)

 One this is done, the ECU transmits a 55h to the tester at
 the speed it wishes to communicate and waits a short 100's of millisecs
 delay for the tester to setup the baud..

 The ECU then sends TWO "key bytes" which specify WHICH PROTOCOL and WHAT
 OEM .. the Tester transmits the inverse of the last keybyte..

 VOILA.. DONE.. 

 Everything else is part of the KEYWORD PROTOCOL involved..

 The PROTOCOLS (Except for public ones like KW 2000, and CARB/OBD-II stuff)
 are proprietary to the manufacturer and held by FAKRA in Germany

 All FAKRA will tell you, is a list of the keywords and whom they belong
 to.. each protocol is (of course) different..

 Knowing ONE in no case tells you anything about another!

 Jim

 PS: I'm sorry to be so anal about this stuff, but I'd rather not have 
     someone run off on a wild goose chase.. to FULLY support ISO-9141 and 9141/2
     is a very hard thing to do... especially when the spec is wrong/incomplete