FreeDIACOM ? (long)

[Oleg Gusev]

Hi,

 i think i'm not the only one who is surprised by
 annoyingly high price for ( IMHO ) simple software like DIACOM,
 and the absence of the publicly available protocol
 specifications. So i decided to write the specification and
 reference implementation for Linux at least for communication
 with Chrysler SBEC which i have.
 As far as i understand my SBEC uses TTL level asynchronous,
 half-duplex, 7812 baud, no parity, one stop bit link.
 The scantool is supposed to send a one byte "function" code
 followed by several "arguments", which would be acknowledged
 by SBEC, and then SBEC would send some "return code(s)" for this
 "function". The number of "arguments" depends on the "function".
 For example,
 1. "function" 0x10 requests stored error codes and doesn't
     have any "arguments"
 2. "function" 0x17 requests flushing of all stored
     error codes ( also no "arguments" )
 3. "function" 0x13 requests running built-in test, and
     has one "argument" - the number of the test.
 4. "function" 0x14 requests realtime sensor data, also
     has one "argument" - which sensor data to query.
 5. "function" 0x1a requests switch/relay data ( on/off ),
     has one "argument" to identify the switch/relay.

 Do other "functions" exist ? This question is open.
 The available "functions", the "arguments" they accept, the
 meaning/units of "return code" and the hardware link
 protocol may depend on engine/year/etc., so to create a full list
 of available options would take some effort from all interested :-)
 I should try to write this list at least for my SBEC
 ( 3.0 Mitsubishi engine, 1990 ) during this weekend, so
 everybody can get a feeling how it looks like and where to look for.
 The DIACOM owners can help a lot by feeding DIACOM (with the help of
 the debugger) with the fake input from the SBEC at some "magic"
 places, so the relation between "return code" and the sensor data
 value in Volts/Degrees/Steps/Percent/etc could be obtained.
 There seems to be a lot of DIACOM GM users around, and i'm pretty
 surprised that the people having enough qualification and patience
 to diassemble ECU PROMs have not written the realtime monitoring
 stuff...

 Best regards,
              Oleg.

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